diff options
author | filliatr <filliatr@85f007b7-540e-0410-9357-904b9bb8a0f7> | 2003-09-25 14:44:59 +0000 |
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committer | filliatr <filliatr@85f007b7-540e-0410-9357-904b9bb8a0f7> | 2003-09-25 14:44:59 +0000 |
commit | dac8909686ba0c79e5fa35c9b04122b6f5f81e02 (patch) | |
tree | 093b44b54334cfc06a079957db063ad824797d5a | |
parent | 2749f4b0fdf26cd298af4217d884246803f899e4 (diff) |
passage V8
git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@8339 85f007b7-540e-0410-9357-904b9bb8a0f7
-rw-r--r-- | doc/Makefile | 10 | ||||
-rwxr-xr-x | doc/Tutorial.tex | 393 | ||||
-rw-r--r-- | doc/faq.tex | 249 |
3 files changed, 342 insertions, 310 deletions
diff --git a/doc/Makefile b/doc/Makefile index 8a0553419..ae057235a 100644 --- a/doc/Makefile +++ b/doc/Makefile @@ -346,3 +346,13 @@ doc-www-install: (cd $(WWWDOCDIR); rm -f node*.html main*.html toc.html \ tutorial.html changes.html cover.html) cp www/* $(WWWDOCDIR) + +# traducteur V7 -> V8 +tradv8: tradv8.ml4 + ocamlopt.opt -o $@ str.cmxa unix.cmxa -pp "camlp4o -impl" -impl $^ + +v8: tradv8 + for f in `grep -l coq_exa *tex`; do \ + echo $$f; \ + ./tradv8 $$f; mv $$f $$f.save; mv $$f.v8 $$f; \ + done diff --git a/doc/Tutorial.tex b/doc/Tutorial.tex index 60812f353..661169d6a 100755 --- a/doc/Tutorial.tex +++ b/doc/Tutorial.tex @@ -121,14 +121,14 @@ hypotheses and definitions. It will also give a convenient way to reset part of the development. \begin{coq_example} - Section Declaration. +Section Declaration. \end{coq_example} With what we already know, we may now enter in the system a declaration, corresponding to the informal mathematics {\sl let n be a natural number}. \begin{coq_example} -Variable n:nat. +Variable n : nat. \end{coq_example} If we want to translate a more precise statement, such as @@ -137,7 +137,7 @@ we have to add another declaration, which will declare explicitly the hypothesis \verb:Pos_n:, with specification the proper logical proposition: \begin{coq_example} -Hypothesis Pos_n : (gt n O). +Hypothesis Pos_n : (n > 0)%N. \end{coq_example} Indeed we may check that the relation \verb:gt: is known with the right type @@ -155,7 +155,7 @@ with the (abstract) type \verb:Prop: of logical propositions through the arrow function constructor, in order to get a functional type \verb:nat->Prop:: \begin{coq_example} -Check nat->Prop. +Check (nat -> Prop). \end{coq_example} which may be composed again with \verb:nat: in order to obtain the type \verb:nat->nat->Prop: of binary relations over natural numbers. @@ -169,7 +169,7 @@ the expression \verb:(gt n): is well-formed of type \verb:nat->Prop:, and thus that the expression \verb:(gt n O):, which abbreviates \verb:((gt n) O):, is a well-formed proposition. \begin{coq_example} -Check (gt n O). +Check (n > 0)%N. \end{coq_example} \subsection{Definitions} @@ -186,12 +186,12 @@ Definition one := (S O). \end{coq_example} We may optionally indicate the required type: \begin{coq_example} -Definition two : nat := (S one). +Definition two : nat := S one. \end{coq_example} Actually \Coq~ allows several possible syntaxes: \begin{coq_example} -Definition three := (S two) : nat. +Definition three : nat := S two. \end{coq_example} Here is a way to define the doubling function, which expects an @@ -199,7 +199,7 @@ argument \verb:m: of type \verb:nat: in order to build its result as \verb:(plus m m):: \begin{coq_example} -Definition double := [m:nat](plus m m). +Definition double (m:nat) := (m + m)%N. \end{coq_example} The abstraction brackets are explained as follows. The expression \verb+[x:A]e+ is well formed of type \verb+A->B+ in a context @@ -213,7 +213,7 @@ Bound (local) variables and free (global) variables may be mixed. For instance, we may define the function which adds the constant \verb:n: to its argument as \begin{coq_example} -Definition add_n := [m:nat](plus m n). +Definition add_n (m:nat) := (m + n)%N. \end{coq_example} However, note that here we may not rename the formal argument $m$ into $n$ without capturing the free occurrence of $n$, and thus changing the meaning @@ -228,7 +228,7 @@ operator is available in \Coq, with the following syntax: binding, we are obliged to declare explicitly the type of the quantified variable. We check: \begin{coq_example} -Check (m:nat)(gt m O). +Check (forall m:nat, (m > 0)%N). \end{coq_example} We may clean-up the development by removing the contents of the current section: @@ -244,7 +244,7 @@ introducing these atoms as global variables declared of type \verb:Prop:. It is easy to declare several names with the same specification: \begin{coq_example} Section Minimal_Logic. -Variables A,B,C:Prop. +Variables A B C : Prop. \end{coq_example} We shall consider simple implications, such as $A\ra B$, read as @@ -252,7 +252,7 @@ We shall consider simple implications, such as $A\ra B$, read as has been used above as the functionality type constructor, and which may be used as well as propositional connective: \begin{coq_example} -Check A->B. +Check (A -> B). \end{coq_example} Let us now embark on a simple proof. We want to prove the easy tautology @@ -260,7 +260,7 @@ $((A\ra (B\ra C))\ra (A\ra B)\ra (A\ra C)$. We enter the proof engine by the command \verb:Goal:, followed by the conjecture we want to verify: \begin{coq_example} -Goal (A->(B->C))->(A->B)->(A->C). +Goal (A -> B -> C) -> (A -> B) -> A -> C. \end{coq_example} The system displays the current goal below a double line, local hypotheses @@ -277,7 +277,7 @@ For instance, the \verb:Intro: tactic is applicable to any judgment whose goal is an implication, by moving the proposition to the left of the application to the list of local hypotheses: \begin{coq_example} -Intro H. +intro H. \end{coq_example} %{\bf Warning} to users of \Coq~ previous versions: The display of a sequent in @@ -286,14 +286,14 @@ Intro H. Several introductions may be done in one step: \begin{coq_example} -Intros H' HA. +intros H' HA. \end{coq_example} We notice that $C$, the current goal, may be obtained from hypothesis \verb:H:, provided the truth of $A$ and $B$ are established. The tactic \verb:Apply: implements this piece of reasoning: \begin{coq_example} -Apply H. +apply H. \end{coq_example} We are now in the situation where we have two judgments as conjectures @@ -306,19 +306,19 @@ the judgments it generated. In order to solve the current goal, we just have to notice that it is exactly available as hypothesis $HA$: \begin{coq_example} -Exact HA. +exact HA. \end{coq_example} Now $H'$ applies: \begin{coq_example} -Apply H'. +apply H'. \end{coq_example} And we may now conclude the proof as before, with \verb:Exact HA.: Actually, we may not bother with the name \verb:HA:, and just state that the current goal is solvable from the current local assumptions: \begin{coq_example} -Assumption. +assumption. \end{coq_example} The proof is now finished. We may either discard it, by using the @@ -335,7 +335,7 @@ commands used in the proof. % ligne blanche apres Exact HA?? Let us redo the same proof with a few variations. First of all we may name the initial goal as a conjectured lemma: \begin{coq_example} -Lemma distr_impl : (A->(B->C))->(A->B)->(A->C). +Lemma distr_impl : (A -> B -> C) -> (A -> B) -> A -> C. \end{coq_example} %{\bf Warning} to users of \Coq~ older versions: In order to enter the proof @@ -345,7 +345,7 @@ Next, we may omit the names of local assumptions created by the introduction tactics, they can be automatically created by the proof engine as new non-clashing names. \begin{coq_example} -Intros. +intros. \end{coq_example} The \verb:Intros: tactic, with no arguments, effects as many individual @@ -364,12 +364,12 @@ goal, and then tactic $T_1$ to the first newly generated subgoal, We may thus complete the proof of \verb:distr_impl: with one composite tactic: \begin{coq_example} -Apply H; [Assumption | Apply H0; Assumption]. +apply H; [ assumption | apply H0; assumption ]. \end{coq_example} Let us now save lemma \verb:distr_impl:: \begin{coq_example} -Save. +Qed. \end{coq_example} Here \verb:Save: needs no argument, since we gave the name \verb:distr_impl: @@ -381,8 +381,8 @@ Actually, such an easy combination of tactics \verb:Intro:, \verb:Apply: and \verb:Assumption: may be found completely automatically by an automatic tactic, called \verb:Auto:, without user guidance: \begin{coq_example} -Lemma distr_imp : (A->(B->C))->(A->B)->(A->C). -Auto. +Lemma distr_imp : (A -> B -> C) -> (A -> B) -> A -> C. +auto. \end{coq_example} This time, we do not save the proof, we just discard it with the \verb:Abort: @@ -424,26 +424,26 @@ connective. Let us show how to use these ideas for the propositional connectives \begin{coq_example} Lemma and_commutative : A /\ B -> B /\ A. -Intro. +intro. \end{coq_example} We make use of the conjunctive hypothesis \verb:H: with the \verb:Elim: tactic, which breaks it into its components: \begin{coq_example} -Elim H. +elim H. \end{coq_example} We now use the conjunction introduction tactic \verb:Split:, which splits the conjunctive goal into the two subgoals: \begin{coq_example} -Split. +split. \end{coq_example} and the proof is now trivial. Indeed, the whole proof is obtainable as follows: \begin{coq_example} Restart. -Intro H; Elim H; Auto. -Save. +intro H; elim H; auto. +Qed. \end{coq_example} The tactic \verb:Auto: succeeded here because it knows as a hint the @@ -467,14 +467,14 @@ In a similar fashion, let us consider disjunction: \begin{coq_example} Lemma or_commutative : A \/ B -> B \/ A. -Intro H; Elim H. +intro H; elim H. \end{coq_example} Let us prove the first subgoal in detail. We use \verb:Intro: in order to be left to prove \verb:B\/A: from \verb:A:: \begin{coq_example} -Intro HA. +intro HA. \end{coq_example} Here the hypothesis \verb:H: is not needed anymore. We could choose to @@ -482,7 +482,7 @@ actually erase it with the tactic \verb:Clear:; in this simple proof it does not really matter, but in bigger proof developments it is useful to clear away unnecessary hypotheses which may clutter your screen. \begin{coq_example} -Clear H. +clear H. \end{coq_example} The disjunction connective has two introduction rules, since \verb:P\/Q: @@ -491,8 +491,8 @@ proof constructors are called respectively \verb:or_introl: and \verb:or_intror:; they are applied to the current goal by tactics \verb:Left: and \verb:Right: respectively. For instance: \begin{coq_example} -Right. -Trivial. +right. +trivial. \end{coq_example} The tactic \verb:Trivial: works like \verb:Auto: with the hints database, but it only tries those tactics that can solve the goal in one @@ -502,7 +502,7 @@ As before, all these tedious elementary steps may be performed automatically, as shown for the second symmetric case: \begin{coq_example} -Auto. +auto. \end{coq_example} However, \verb:Auto: alone does not succeed in proving the full lemma, because @@ -519,8 +519,8 @@ tautologies is indeed available in \Coq~ as the \verb:Tauto: tactic. %called ``Dyckhoff'': \begin{coq_example} Restart. -Tauto. -Save. +tauto. +Qed. \end{coq_example} It is possible to inspect the actual proof tree constructed by \verb:Tauto:, @@ -544,9 +544,9 @@ naive user of \Coq~ may safely ignore these formal details. Let us exercise the \verb:Tauto: tactic on a more complex example: \begin{coq_example} -Lemma distr_and : A->(B/\C) -> (A->B) /\ (A->C). -Tauto. -Save. +Lemma distr_and : A -> B /\ C -> (A -> B) /\ (A -> C). +tauto. +Qed. \end{coq_example} \subsection{Classical reasoning} @@ -554,8 +554,8 @@ Save. \verb:Tauto: always comes back with an answer. Here is an example where it fails: \begin{coq_example} -Lemma Peirce : ((A->B)->A)->A. -Try Tauto. +Lemma Peirce : ((A -> B) -> A) -> A. +try tauto. \end{coq_example} Note the use of the \verb:Try: tactical, which does nothing if its tactic @@ -567,9 +567,9 @@ every truth-assignment to \verb:A: and \verb:B:. Indeed the double negation of Peirce's law may be proved in \Coq~ using \verb:Tauto:: \begin{coq_example} Abort. -Lemma NNPeirce : ~~(((A->B)->A)->A). -Tauto. -Save. +Lemma NNPeirce : ~ ~ (((A -> B) -> A) -> A). +tauto. +Qed. \end{coq_example} In classical logic, the double negation of a proposition is equivalent to this @@ -579,16 +579,16 @@ want to use classical logic in \Coq, you have to import explicitly the of excluded middle, and classical tautologies such as de Morgan's laws. The \verb:Require: command is used to import a module from \Coq's library: \begin{coq_example} -Require Classical. +Require Import Classical. Check NNPP. \end{coq_example} and it is now easy (although admittedly not the most direct way) to prove a classical law such as Peirce's: \begin{coq_example} -Lemma Peirce : ((A->B)->A)->A. -Apply NNPP; Tauto. -Save. +Lemma Peirce : ((A -> B) -> A) -> A. +apply NNPP; tauto. +Qed. \end{coq_example} Here is one more example of propositional reasoning, in the shape of @@ -604,16 +604,16 @@ a Scottish puzzle. A private club has the following rules: Now, we show that these rules are so strict that no one can be accepted. \begin{coq_example} Section club. -Variable Scottish, RedSocks, WearKilt, Married, GoOutSunday : Prop. -Hypothesis rule1 : ~Scottish -> RedSocks. -Hypothesis rule2 : WearKilt \/ ~RedSocks. -Hypothesis rule3 : Married -> ~GoOutSunday. +Variables Scottish RedSocks WearKilt Married GoOutSunday : Prop. +Hypothesis rule1 : ~ Scottish -> RedSocks. +Hypothesis rule2 : WearKilt \/ ~ RedSocks. +Hypothesis rule3 : Married -> ~ GoOutSunday. Hypothesis rule4 : GoOutSunday <-> Scottish. -Hypothesis rule5 : WearKilt -> (Scottish /\ Married). +Hypothesis rule5 : WearKilt -> Scottish /\ Married. Hypothesis rule6 : Scottish -> WearKilt. Lemma NoMember : False. -Tauto. -Save. +tauto. +Qed. \end{coq_example} At that point \verb:NoMember: is a proof of the absurdity depending on hypotheses. @@ -659,8 +659,8 @@ notions local to a well-delimited scope. We start by assuming a domain of discourse \verb:D:, and a binary relation \verb:R: over \verb:D:: \begin{coq_example} Section Predicate_calculus. -Variable D:Set. -Variable R: D -> D -> Prop. +Variable D : Set. +Variable R : D -> D -> Prop. \end{coq_example} As a simple example of predicate calculus reasoning, let us assume @@ -671,8 +671,8 @@ a theory, but rather local hypotheses to a theorem, we open a specific section to this effect. \begin{coq_example} Section R_sym_trans. -Hypothesis R_symmetric : (x,y:D) (R x y) -> (R y x). -Hypothesis R_transitive : (x,y,z:D) (R x y) -> (R y z) -> (R x z). +Hypothesis R_symmetric : forall x y:D, R x y -> R y x. +Hypothesis R_transitive : forall x y z:D, R x y -> R y z -> R x z. \end{coq_example} Remark the syntax \verb+(x:D)+ which stands for universal quantification @@ -682,7 +682,7 @@ $\forall x : D$. We now state our lemma, and enter proof mode. \begin{coq_example} -Lemma refl_if : (x:D)(EX y | (R x y)) -> (R x x). +Lemma refl_if : forall x:D, ( EX y : _ | R x y) -> R x x. \end{coq_example} Remark that the hypotheses which are local to the currently opened sections @@ -705,7 +705,7 @@ tactic \verb:Exists:, and its elimination provides a witness \verb+a:D+ to \verb:P:, together with an assumption \verb+h:(P a)+ that indeed \verb+a+ verifies \verb:P:. Let us see how this works on this simple example. \begin{coq_example} -Intros x x_Rlinked. +intros x x_Rlinked. \end{coq_example} Remark that \verb:Intro: treats universal quantification in the same way @@ -716,11 +716,11 @@ we would have obtained the goal: Undo. \end{coq_eval} \begin{coq_example} -Intro y. +intro y. \end{coq_example} \begin{coq_eval} Undo. -Intros x x_Rlinked. +intros x x_Rlinked. \end{coq_eval} Let us now use the existential hypothesis \verb:x_Rlinked: to @@ -728,8 +728,8 @@ exhibit an R-successor y of x. This is done in two steps, first with \verb:Elim:, then with \verb:Intros: \begin{coq_example} -Elim x_Rlinked. -Intros y Rxy. +elim x_Rlinked. +intros y Rxy. \end{coq_example} Now we want to use \verb:R_transitive:. The \verb:Apply: tactic will know @@ -738,21 +738,21 @@ help on how to instantiate \verb:y:, which appear in the hypotheses of \verb:R_transitive:, but not in its conclusion. We give the proper hint to \verb:Apply: in a \verb:with: clause, as follows: \begin{coq_example} -Apply R_transitive with y. +apply R_transitive with y. \end{coq_example} The rest of the proof is routine: \begin{coq_example} -Assumption. -Apply R_symmetric; Assumption. +assumption. +apply R_symmetric; assumption. \end{coq_example} \begin{coq_example*} -Save. +Qed. \end{coq_example*} Let us now close the current section. \begin{coq_example} -End R_sym_trans. +End R_sym_trans. \end{coq_example} Here \Coq's printout is a warning that all local hypotheses have been @@ -774,16 +774,16 @@ Let us illustrate this feature by pursuing our \verb:Predicate_calculus: section with an enrichment of our language: we declare a unary predicate \verb:P: and a constant \verb:d:: \begin{coq_example} -Variable P:D->Prop. -Variable d:D. +Variable P : D -> Prop. +Variable d : D. \end{coq_example} We shall now prove a well-known fact from first-order logic: a universal predicate is non-empty, or in other terms existential quantification follows from universal quantification. \begin{coq_example} -Lemma weird : ((x:D)(P x)) -> (EX a | (P a)). -Intro UnivP. +Lemma weird : (forall x:D, P x) -> EX a : _ | P a. + intro UnivP. \end{coq_example} First of all, notice the pair of parentheses around \verb+(x:D)(P x)+ in @@ -807,8 +807,8 @@ the predicate. Let us conclude the proof, in order to show the use of the \verb:Exists: tactic: \begin{coq_example} -Exists d; Trivial. -Save. +exists d; trivial. +Qed. \end{coq_example} Another fact which illustrates the sometimes disconcerting rules of @@ -820,51 +820,51 @@ We shall need classical reasoning. Instead of loading the \verb:Classical: module as we did above, we just state the law of excluded middle as a local hypothesis schema at this point: \begin{coq_example} -Hypothesis EM : (A:Prop) A \/ ~A. -Lemma drinker : (EX x | (P x) -> (x:D)(P x)). +Hypothesis EM : forall A:Prop, A \/ ~ A. +Lemma drinker : EX x : _ | P x -> forall x:D, P x. \end{coq_example} The proof goes by cases on whether or not there is someone who does not drink. Such reasoning by cases proceeds by invoking the excluded middle principle, via \verb:Elim: of the proper instance of \verb:EM:: \begin{coq_example} -Elim (EM (EX x | ~(P x))). +elim (EM ( EX x : _ | ~ P x)). \end{coq_example} We first look at the first case. Let Tom be the non-drinker: \begin{coq_example} -Intro Non_drinker; Elim Non_drinker; Intros Tom Tom_does_not_drink. +intro Non_drinker; elim Non_drinker; intros Tom Tom_does_not_drink. \end{coq_example} We conclude in that case by considering Tom, since his drinking leads to a contradiction: \begin{coq_example} -Exists Tom; Intro Tom_drinks. +exists Tom; intro Tom_drinks. \end{coq_example} There are several ways in which we may eliminate a contradictory case; a simple one is to use the \verb:Absurd: tactic as follows: \begin{coq_example} -Absurd (P Tom); Trivial. +absurd (P Tom); trivial. \end{coq_example} We now proceed with the second case, in which actually any person will do; such a John Doe is given by the non-emptiness witness \verb:d:: \begin{coq_example} -Intro No_nondrinker; Exists d; Intro d_drinks. +intro No_nondrinker; exists d; intro d_drinks. \end{coq_example} Now we consider any Dick in the bar, and reason by cases according to its drinking or not: \begin{coq_example} -Intro Dick; Elim (EM (P Dick)); Trivial. +intro Dick; elim (EM (P Dick)); trivial. \end{coq_example} The only non-trivial case is again treated by contradiction: \begin{coq_example} -Intro Dick_does_not_drink; Absurd (EX x | ~(P x)); Trivial. -Exists Dick; Trivial. -Save. +intro Dick_does_not_drink; absurd ( EX x : _ | ~ P x); trivial. +exists Dick; trivial. +Qed. \end{coq_example} Now, let us close the main section: @@ -906,10 +906,12 @@ in order to get a more general induction hypothesis. The tactic \begin{coq_example} Section Predicate_Calculus. -Variable P,Q:nat->Prop. Variable R: nat->nat->Prop. -Lemma PQR : (x,y:nat)((R x x)->(P x)->(Q x))->(P x)->(R x y)->(Q x). -Intros. -Generalize H0. +Variables P Q : nat -> Prop. +Variable R : nat -> nat -> Prop. +Lemma PQR : + forall x y:nat, (R x x -> P x -> Q x) -> P x -> R x y -> Q x. +intros. +generalize H0. \end{coq_example} Sometimes it may be convenient to use a lemma, although we do not have @@ -917,7 +919,7 @@ a direct way to appeal to such an already proven fact. The tactic \verb:Cut: permits to use the lemma at this point, keeping the corresponding proof obligation as a new subgoal: \begin{coq_example} -Cut (R x x); Trivial. +cut (R x x); trivial. \end{coq_example} \subsection{Equality} @@ -931,31 +933,31 @@ and \verb:Replace:. Let us give a few examples of equality replacement. Let us assume that some arithmetic function \verb:f: is null in zero: \begin{coq_example} -Variable f:nat->nat. -Hypothesis foo : (f O)=O. +Variable f : nat -> nat. +Hypothesis foo : f 0 = 0%N. \end{coq_example} We want to prove the following conditional equality: \begin{coq_example*} -Lemma L1 : (k:nat)k=O->(f k)=k. +Lemma L1 : forall k:nat, k = 0%N -> f k = k. \end{coq_example*} As usual, we first get rid of local assumptions with \verb:Intro:: \begin{coq_example} -Intros k E. +intros k E. \end{coq_example} Let us now use equation \verb:E: as a left-to-right rewriting: \begin{coq_example} -Rewrite E. +rewrite E. \end{coq_example} This replaced both occurrences of \verb:k: by \verb:O:. Now \verb:Apply foo: will finish the proof: \begin{coq_example} -Apply foo. -Save. +apply foo. +Qed. \end{coq_example} When one wants to rewrite an equality in a right to left fashion, we should @@ -963,9 +965,9 @@ use \verb:Rewrite <- E: rather than \verb:Rewrite E: or the equivalent \verb:Rewrite -> E:. Let us now illustrate the tactic \verb:Replace:. \begin{coq_example} -Hypothesis f10 : (f (S O))=(f O). -Lemma L2 : (f (f (S O)))=O. -Replace (f (S O)) with O. +Hypothesis f10 : f 1 = f 0. +Lemma L2 : f (f 1) = 0%N. +replace (f 1) with 0%N. \end{coq_example} What happened here is that the replacement left the first subgoal to be proved, but another proof obligation was generated by the \verb:Replace: @@ -974,8 +976,8 @@ by applying lemma \verb:foo:; the second one transitivity and then symmetry of equality, for instance with tactics \verb:Transitivity: and \verb:Symmetry:: \begin{coq_example} -Apply foo. -Transitivity (f O); Symmetry; Trivial. +apply foo. +transitivity (f 0); symmetry; trivial. \end{coq_example} In case the equality $t=u$ generated by \verb:Replace: $u$ \verb:with: $t$ is an assumption @@ -983,9 +985,9 @@ $t$ is an assumption corresponding goal will not appear. For instance: \begin{coq_example} Restart. -Replace (f O) with O. -Rewrite f10; Rewrite foo; Trivial. -Save. +replace (f 0) with 0%N. +rewrite f10; rewrite foo; trivial. +Qed. \end{coq_example} @@ -998,7 +1000,7 @@ abstract Types. In order to develop such abstract reasoning, one must load the library \verb:Logic_Type:. \begin{coq_example} -Require Logic_Type. +Require Import Logic_Type. \end{coq_example} New proof combinators are now available, such as the existential @@ -1006,7 +1008,7 @@ quantification \verb:exT: over a Type, available with syntax \verb:(EXT x | (P x)):. The corresponding introduction combinator may be invoked by the tactic \verb:Exists: as above. \begin{coq_example} -Check exT_intro. +Check ex_intro. \end{coq_example} Similarly, equality over Type is available, with notation @@ -1029,62 +1031,63 @@ Assume that we want to develop the theory of sets represented as characteristic predicates over some universe \verb:U:. For instance: %CP Une petite explication pour le codage de element ? \begin{coq_example} -Variable U:Type. -Definition set := U->Prop. -Definition element := [x:U][S:set](S x). -Definition subset := [A,B:set](x:U)(element x A)->(element x B). +Variable U : Type. +Definition set := U -> Prop. +Definition element (x:U) (S:set) := S x. +Definition subset (A B:set) := forall x:U, element x A -> element x B. \end{coq_example} Now, assume that we have loaded a module of general properties about relations over some abstract type \verb:T:, such as transitivity: \begin{coq_example} -Definition transitive := [T:Type][R:T->T->Prop] - (x,y,z:T)(R x y)->(R y z)->(R x z). +Definition transitive (T:Type) (R:T -> T -> Prop) := + forall x y z:T, R x y -> R y z -> R x z. \end{coq_example} Now, assume that we want to prove that \verb:subset: is a \verb:transitive: relation. \begin{coq_example} -Lemma subset_transitive : (transitive set subset). +Lemma subset_transitive : transitive set subset. \end{coq_example} In order to make any progress, one needs to use the definition of \verb:transitive:. The \verb:Unfold: tactic, which replaces all occurrences of a defined notion by its definition in the current goal, may be used here. \begin{coq_example} -Unfold transitive. +unfold transitive. \end{coq_example} Now, we must unfold \verb:subset:: \begin{coq_example} -Unfold subset. +unfold subset. \end{coq_example} Now, unfolding \verb:element: would be a mistake, because indeed a simple proof can be found by \verb:Auto:, keeping \verb:element: an abstract predicate: \begin{coq_example} -Auto. +auto. \end{coq_example} Many variations on \verb:Unfold: are provided in \Coq. For instance, we may selectively unfold one designated occurrence: \begin{coq_example} Undo 2. -Unfold 2 subset. +unfold subset 2. \end{coq_example} One may also unfold a definition in a given local hypothesis, using the \verb:in: notation: \begin{coq_example} -Intros. -Unfold subset in H. +intros. +unfold subset in H. \end{coq_example} Finally, the tactic \verb:Red: does only unfolding of the head occurrence of the current goal: \begin{coq_example} -Red. -Auto. Save. +red. +auto. +Qed. \end{coq_example} @@ -1117,7 +1120,9 @@ mathematical constructions. Let us start with the collection of booleans, as they are specified in the \Coq's \verb:Prelude: module: \begin{coq_example} -Inductive bool : Set := true : bool | false : bool. +Inductive bool : Set := + | true : bool + | false : bool. \end{coq_example} Such a declaration defines several objects at once. First, a new @@ -1139,21 +1144,21 @@ Check bool_rect. Let us for instance prove that every Boolean is true or false. \begin{coq_example} -Lemma duality : (b:bool)(b=true \/ b=false). -Intro b. +Lemma duality : forall b:bool, b = true \/ b = false. +intro b. \end{coq_example} We use the knowledge that \verb:b: is a \verb:bool: by calling tactic \verb:Elim:, which is this case will appeal to combinator \verb:bool_ind: in order to split the proof according to the two cases: \begin{coq_example} -Elim b. +elim b. \end{coq_example} It is easy to conclude in each case: \begin{coq_example} -Left; Trivial. -Right; Trivial. +left; trivial. +right; trivial. \end{coq_example} Indeed, the whole proof can be done with the combination of the @@ -1161,8 +1166,8 @@ Indeed, the whole proof can be done with the combination of the with good old \verb:Auto:: \begin{coq_example} Restart. -Induction b; Auto. -Save. +oldinduction b; auto. +Qed. \end{coq_example} \subsection{Natural numbers} @@ -1170,7 +1175,9 @@ Save. Similarly to Booleans, natural numbers are defined in the \verb:Prelude: module with constructors \verb:S: and \verb:O:: \begin{coq_example} -Inductive nat : Set := O : nat | S : nat->nat. +Inductive nat : Set := + | O : nat + | S : nat -> nat. \end{coq_example} The elimination principles which are automatically generated are Peano's @@ -1183,7 +1190,7 @@ Check nat_rec. Let us start by showing how to program the standard primitive recursion operator \verb:prim_rec: from the more general \verb:nat_rec:: \begin{coq_example} -Definition prim_rec := (nat_rec [i:nat]nat). +Definition prim_rec := nat_rec (fun i:nat => nat). \end{coq_example} That is, instead of computing for natural \verb:i: an element of the indexed @@ -1199,15 +1206,15 @@ get an apparently more complicated expression. Indeed the type of be checked in \Coq~ by command \verb:Eval Cbv Beta:, which $\beta$-reduces an expression to its {\sl normal form}: \begin{coq_example} -Eval Cbv Beta in - ([_:nat]nat O) - ->((y:nat)([_:nat]nat y)->([_:nat]nat (S y))) - ->(n:nat)([_:nat]nat n). +Eval cbv beta in + ((fun _:nat => nat) O -> + (forall y:nat, (fun _:nat => nat) y -> (fun _:nat => nat) (S y)) -> + forall n:nat, (fun _:nat => nat) n). \end{coq_example} Let us now show how to program addition with primitive recursion: \begin{coq_example} -Definition addition := [n,m:nat](prim_rec m [p:nat][rec:nat](S rec) n). +Definition addition (n m:nat) := prim_rec m (fun p rec:nat => S rec) n. \end{coq_example} That is, we specify that \verb+(addition n m)+ computes by cases on \verb:n: @@ -1216,7 +1223,7 @@ according to its main constructor; when \verb:n=O:, we get \verb:m:; of the recursive computation \verb+(addition p m)+. Let us verify it by asking \Coq~to compute for us say $2+3$: \begin{coq_example} -Eval Compute in (addition (S (S O)) (S (S (S O)))). +Eval compute in (addition (S (S O)) (S (S (S O)))). \end{coq_example} Actually, we do not have to do all explicitly. {\Coq} provides a @@ -1224,11 +1231,11 @@ special syntax {\tt Fixpoint/Cases} for generic primitive recursion, and we could thus have defined directly addition as: \begin{coq_example} -Fixpoint plus [n:nat] : nat -> nat := - [m:nat]Cases n of - O => m - | (S p) => (S (plus p m)) - end. +Fixpoint plus (n m:nat) {struct n} : nat := + match n with + | O => m + | S p => S (plus p m) + end. \end{coq_example} For the rest of the session, we shall clean up what we did so far with @@ -1252,8 +1259,8 @@ Let us now show how to do proofs by structural induction. We start with easy properties of the \verb:plus: function we just defined. Let us first show that $n=n+0$. \begin{coq_example} -Lemma plus_n_O : (n:nat)n=(plus n O). -Intro n; Elim n. +Lemma plus_n_O : forall n:nat, n = (n + 0)%N. +intro n; elim n. \end{coq_example} What happened was that \verb:Elim n:, in order to construct a \verb:Prop: @@ -1268,14 +1275,14 @@ argument starts with a constructor, and is thus amenable to simplification by primitive recursion. The \Coq~tactic \verb:Simpl: can be used for this purpose: \begin{coq_example} -Simpl. -Auto. +simpl. +auto. \end{coq_example} We proceed in the same way for the base step: \begin{coq_example} -Simpl; Auto. -Save. +simpl; auto. +Qed. \end{coq_example} Here \verb:Auto: succeeded, because it used as a hint lemma \verb:eq_S:, @@ -1287,13 +1294,13 @@ Check eq_S. Actually, let us see how to declare our lemma \verb:plus_n_O: as a hint to be used by \verb:Auto:: \begin{coq_example} -Hints Resolve plus_n_O. +Hints Resolve plus_n_O . \end{coq_example} We now proceed to the similar property concerning the other constructor \verb:S:: \begin{coq_example} -Lemma plus_n_S : (n,m:nat)(S (plus n m))=(plus n (S m)). +Lemma plus_n_S : forall n m:nat, S (n + m) = (n + S m)%N. \end{coq_example} We now go faster, remembering that tactic \verb:Induction: does the @@ -1301,21 +1308,21 @@ necessary \verb:Intros: before applying \verb:Elim:. Factoring simplification and automation in both cases thanks to tactic composition, we prove this lemma in one line: \begin{coq_example} -Induction n; Simpl; Auto. -Save. -Hints Resolve plus_n_S. +oldinduction n; simpl; auto. +Qed. +Hints Resolve plus_n_S . \end{coq_example} Let us end this exercise with the commutativity of \verb:plus:: \begin{coq_example} -Lemma plus_com : (n,m:nat)(plus n m)=(plus m n). +Lemma plus_com : forall n m:nat, (n + m)%N = (m + n)%N. \end{coq_example} Here we have a choice on doing an induction on \verb:n: or on \verb:m:, the situation being symmetric. For instance: \begin{coq_example} -Induction m; Simpl; Auto. +oldinduction m; simpl; auto. \end{coq_example} Here \verb:Auto: succeeded on the base case, thanks to our hint @@ -1323,8 +1330,8 @@ Here \verb:Auto: succeeded on the base case, thanks to our hint \verb:Auto: does not handle: \begin{coq_example} -Intros m' E; Rewrite <- E; Auto. -Save. +intros m' E; rewrite <- E; auto. +Qed. \end{coq_example} \subsection{Discriminate} @@ -1335,16 +1342,18 @@ the constructors \verb:O: and \verb:S:: it computes to \verb:False: when its argument is \verb:O:, and to \verb:True: when its argument is of the form \verb:(S n):: \begin{coq_example} -Definition Is_S - := [n:nat]Cases n of O => False | (S p) => True end. +Definition Is_S (n:nat) := match n with + | O => False + | S p => True + end. \end{coq_example} Now we may use the computational power of \verb:Is_S: in order to prove trivially that \verb:(Is_S (S n)):: \begin{coq_example} -Lemma S_Is_S : (n:nat)(Is_S (S n)). -Simpl; Trivial. -Save. +Lemma S_Is_S : forall n:nat, Is_S (S n). +simpl; trivial. +Qed. \end{coq_example} But we may also use it to transform a \verb:False: goal into @@ -1352,26 +1361,26 @@ But we may also use it to transform a \verb:False: goal into we want to prove that \verb:O: and \verb:S: construct different values, one of Peano's axioms: \begin{coq_example} -Lemma no_confusion : (n:nat)~(O=(S n)). +Lemma no_confusion : forall n:nat, 0%N <> S n. \end{coq_example} First of all, we replace negation by its definition, by reducing the goal with tactic \verb:Red:; then we get contradiction by successive \verb:Intros:: \begin{coq_example} -Red; Intros n H. +red; intros n H. \end{coq_example} Now we use our trick: \begin{coq_example} -Change (Is_S O). +change (Is_S 0). \end{coq_example} Now we use equality in order to get a subgoal which computes out to \verb:True:, which finishes the proof: \begin{coq_example} -Rewrite H; Trivial. -Simpl; Trivial. +rewrite H; trivial. +simpl; trivial. \end{coq_example} Actually, a specific tactic \verb:Discriminate: is provided @@ -1380,8 +1389,8 @@ explicitly the relevant discrimination predicates: \begin{coq_example} Restart. -Intro n; Discriminate. -Save. +intro n; discriminate. +Qed. \end{coq_example} @@ -1392,9 +1401,9 @@ may define inductive families, and for instance inductive predicates. Here is the definition of predicate $\le$ over type \verb:nat:, as given in \Coq's \verb:Prelude: module: \begin{coq_example*} -Inductive le [n:nat] : nat -> Prop - := le_n : (le n n) - | le_S : (m:nat)(le n m)->(le n (S m)). +Inductive le (n:nat) : nat -> Prop := + | le_n : le n n + | le_S : forall m:nat, le n m -> le n (S m). \end{coq_example*} This definition introduces a new predicate \verb+le:nat->nat->Prop+, @@ -1415,9 +1424,9 @@ Check le_ind. Let us show how proofs may be conducted with this principle. First we show that $n\le m \Rightarrow n+1\le m+1$: \begin{coq_example} -Lemma le_n_S : (n,m:nat)(le n m)->(le (S n) (S m)). -Intros n m n_le_m. -Elim n_le_m. +Lemma le_n_S : forall n m:nat, le n m -> le (S n) (S m). +intros n m n_le_m. +elim n_le_m. \end{coq_example} What happens here is similar to the behaviour of \verb:Elim: on natural @@ -1426,8 +1435,8 @@ which generates the two subgoals, which may then be solved easily %as if ``backchaining'' the current goal with the help of the defining clauses of \verb:le:. \begin{coq_example} -Apply le_n; Trivial. -Intros; Apply le_S; Trivial. +apply le_n; trivial. +intros; apply le_S; trivial. \end{coq_example} Now we know that it is a good idea to give the defining clauses as hints, @@ -1435,7 +1444,7 @@ so that the proof may proceed with a simple combination of \verb:Induction: and \verb:Auto:. \begin{coq_example} Restart. -Hints Resolve le_n le_S. +Hints Resolve le_n le_S . \end{coq_example} We have a slight problem however. We want to say ``Do an induction on @@ -1443,15 +1452,15 @@ hypothesis \verb:(le n m):'', but we have no explicit name for it. What we do in this case is to say ``Do an induction on the first unnamed hypothesis'', as follows. \begin{coq_example} -Induction 1; Auto. -Save. +oldinduction 1; auto. +Qed. \end{coq_example} Here is a more tricky problem. Assume we want to show that $n\le 0 \Rightarrow n=0$. This reasoning ought to follow simply from the fact that only the first defining clause of \verb:le: applies. \begin{coq_example} -Lemma tricky : (n:nat)(le n O)->n=O. +Lemma tricky : forall n:nat, le n 0 -> n = 0%N. \end{coq_example} However, here trying something like \verb:Induction 1: would lead @@ -1463,9 +1472,9 @@ that only \verb:le_n: applies, whence the result. This analysis may be performed by the ``inversion'' tactic \verb:Inversion_clear: as follows: \begin{coq_example} -Intros n H; Inversion_clear H. -Trivial. -Save. +intros n H; inversion_clear H. +trivial. +Qed. \end{coq_example} \chapter{Modules} @@ -1480,7 +1489,7 @@ the library, you have to use the \verb"Require" command, as we saw for classical logic above. For instance, if you want more arithmetic constructions, you should request: \begin{coq_example*} -Require Arith. +Require Import Arith. \end{coq_example*} Such a command looks for a (compiled) module file \verb:Arith.vo: in @@ -1496,7 +1505,7 @@ it resides in eponym subdirectory \verb=Arith= of the standard library, it can be as well required by the command \begin{coq_example*} -Require Coq.Arith.Arith. +Require Import Coq.Arith.Arith. \end{coq_example*} This may be useful to avoid ambiguities if somewhere, in another branch @@ -1547,7 +1556,7 @@ conclusion matching a given pattern, where \verb:?: can be used in place of an arbitrary term. \begin{coq_example} -SearchPattern (plus ? ?)=?. +SearchPattern ((_ + _)%N = _). \end{coq_example} % The argument to give is a type and it searches in the current context all diff --git a/doc/faq.tex b/doc/faq.tex index c69c587b7..0f9173755 100644 --- a/doc/faq.tex +++ b/doc/faq.tex @@ -178,8 +178,10 @@ the result (look at \verb=inj_pair2= in \vfile{\LogicEqdep}{Eqdep}). elimination of reflexive equality proofs. \begin{coq_example*} -Axiom Streicher_K: (U:Type)(x:U)(P:x=x->Prop) - (P (refl_equal ? x))->(p:x=x)(P p). +Axiom + Streicher_K : + forall (U:Type) (x:U) (P:x = x -> Prop), + P (refl_equal x) -> forall p:x = x, P p. \end{coq_example*} In the general case, axiom $K$ is an independent statement of the @@ -192,27 +194,34 @@ Axiom $K$ is equivalent to {\em Uniqueness of Identity Proofs} \cite{HofStr98} which states that \begin{coq_example*} -Axiom UIP: (A:Set)(x,y:A)(p1,p2:x=y)p1==p2. +Axiom UIP : forall (A:Set) (x y:A) (p1 p2:x = y), p1 = p2. \end{coq_example*} Axiom $K$ is also equivalent to {\em Uniqueness of Reflexive Identity Proofs} \cite{HofStr98} \begin{coq_example*} -Axiom UIP_refl: (A:Set)(x:A)(p:x=x)p==(refl_equal A x). +Axiom UIP_refl : forall (A:Set) (x:A) (p:x = x), p = refl_equal x. \end{coq_example*} Axiom $K$ is also equivalent to \begin{coq_example*} -Axiom eq_rec_eq : (A:Set)(a:A)(P:A->Set)(p:(P p))(h:a==a) p=(eq_rect A a P p a h). +Axiom + eq_rec_eq : + forall (A:Set) (a:A) (P:A -> Set) (p:P p) (h:a = a), + p = eq_rect P p h. \end{coq_example*} It is also equivalent to the injectivity of dependent equality (dependent equality is itself equivalent to equality of dependent pairs). \begin{coq_example*} -Inductive eq_dep [U:Set;P:U->Set;p:U;x:(P p)] : (q:U)(P q)->Prop := - eq_dep_intro : (eq_dep U P p x p x). -Axiom eq_dep_eq : (U:Set)(u:U)(P:U->Set)(p1,p2:(P u))(eq_dep U P u p1 u p2)->p1=p2. +Inductive eq_dep (U:Set) (P:U -> Set) (p:U) (x:P p) : +forall q:U, P q -> Prop := + eq_dep_intro : eq_dep U P p x p x. +Axiom + eq_dep_eq : + forall (U:Set) (u:U) (P:U -> Set) (p1 p2:P u), + eq_dep U P u p1 u p2 -> p1 = p2. \end{coq_example*} All of these statements can be found in file \vfile{\LogicEqdep}{Eqdep}. @@ -227,14 +236,16 @@ nat} are discriminable. As discrimination property we take the property to have no more than 2 elements. \begin{coq_example*} -Theorem nat_bool_discr : ~bool==nat. +Theorem nat_bool_discr : bool <> nat. Proof. - Pose discr := [X:Set]~(a,b:X)~(x:X)~x=a->~x=b->False. - Intro Heq; Assert H : (discr bool). - Intro H; Apply (H true false); NewDestruct x; Auto. - Rewrite Heq in H; Apply H; Clear H. - NewDestruct a; NewDestruct b; Intro H0; EAuto. - NewDestruct n; [Apply (H0 (S (S O))); Discriminate | EAuto]. + pose discr := + fun X:Set => + ~ (forall a b:X, ~ (forall x:X, x <> a -> x <> b -> False)). + intro Heq; assert H: discr bool. + intro H; apply (H true false); destruct x; auto. + rewrite Heq in H; apply H; clear H. + destruct a; destruct b; intro H0; eauto. + destruct n; [ apply (H0 2%N); discriminate | eauto ]. Qed. \end{coq_example*} @@ -245,24 +256,28 @@ predicate satisfied by the elements of the sets. As an example we show the following theorem. \begin{coq_example*} -Theorem le_le: (m,n:nat){x:nat | (le x m)} = {x:nat | (le x n)} -> m = n. - -Inductive discr_int_n [n:nat;X:Set] : Prop := - intro : (fst:X->nat)(snd:(x:X)(le (fst x) n)) - ((x,y:X)(exist ? [z](le z n) (fst x) (snd x))= - (exist ? [z](le z n) (fst y) (snd y))->x=y) - -> (discr_int_n n X). - +Theorem le_le : + forall m n:nat, + {x : nat | (x <= m)%N} = {x : nat | (x <= n)%N} -> m = n. +Inductive discr_int_n (n:nat) (X:Set) : Prop := + intro : + forall (fst:X -> nat) (snd:forall x:X, (fst x <= n)%N), + (forall x y:X, + exist (fun z => (z <= n)%N) (fst x) (snd x) = + exist (fun z => (z <= n)%N) (fst y) (snd y) -> x = y) -> + discr_int_n n X. Proof. -Intros. -Assert Hdiscr : (discr_int_n m {x:nat | (le x m)}). -Split with (proj1_sig nat [x:?](le x m)) (proj2_sig nat [x:?](le x m)). -NewDestruct x; NewDestruct y. -Exact [x]x. -Rewrite H in Hdiscr. -Elim Hdiscr. -Assert H1:=(snd (exist nat [z](le z (S n)) (S n) (le_n (S n)))). -(* ... *) +intros. +assert Hdiscr: discr_int_n m ({x : nat | (x <= m)%N}). +split with + (proj1_sig (P:=(fun x => (x <= m)%N))) + (proj2_sig (P:=(fun x => (x <= m)%N))). +destruct x; destruct y. +exact (fun x => x). +rewrite H in Hdiscr. +elim Hdiscr. +assert H1 := + snd (A:=(exist (fun z => (z <= S n)%N) (S n) (le_n (S n)))). \end{coq_example*} \section{Axioms} @@ -283,7 +298,8 @@ Let {\tt A}, {\tt B} be types. To deal with extensionality on own extensional equality on \verb=A->B=. \begin{coq_example*} - Definition ext_eq [f,g:A->B] := (x:A)(f x)=(g x). +Definition ext_eq (f + g:A -> B) := forall x:A, f x = g x. \end{coq_example*} and to reason on \verb=A->B= as a setoid (see the Chapter on @@ -319,8 +335,8 @@ if its constructors embed sets or propositions. As an example, here is a large inductive type: \begin{coq_example*} - Inductive sigST [P:Set->Set] : Set - := existST : (X:Set)(P X) -> (sigST P). +Inductive sigST (P:Set -> Set) : Set := + existST : forall X:Set, P X -> sigST P. \end{coq_example*} Large inductive definition have restricted elimination scheme to @@ -337,9 +353,12 @@ Reset Initial. \end{coq_eval} \begin{coq_example*} - Inductive I : Set := intro : (k:Set)k -> I. - Lemma eq_jdef : (x,y:nat) (intro ? x)=(intro ? y) -> x=y. - Intros x y H; Injection H. +Inductive I : Set := + intro : forall k:Set, k -> I. +Lemma eq_jdef : + forall x y:nat, intro _ x = intro _ y -> x = y. +Proof. + intros x y H; injection H. \end{coq_example*} \answer Injectivity of constructors is restricted to predicative types. If @@ -389,13 +408,13 @@ mergesort} as an example). the arguments of the loop. \begin{coq_example*} -Definition R [a,b:(list nat)] := (length a) < (length b). +Definition R (a b:list nat) := (length a < length b)%N. \end{coq_example*} \item Prove that this order is well-founded (in fact that all elements in {\tt A} are accessible along {\tt R}). \begin{coq_example*} -Lemma Rwf : (well_founded R). +Lemma Rwf : well_founded (A:=R). \end{coq_example*} \item Define the step function (which needs proofs that recursive @@ -416,7 +435,7 @@ Definition merge_step [l:(list nat)][f:(l':(list nat))(R l' l)->(list nat)] := \item Define the recursive function by fixpoint on the step function. \begin{coq_example*} -Definition merge := (fix (list nat) R Rwf [_](list nat) merge_step). +Definition merge := Fix Rwf (fun _ => list nat) merge_step. \end{coq_example*} \end{itemize} @@ -522,15 +541,15 @@ apply the elimination scheme using the \verb=using= option of \answer To reason by induction on pairs, just reason by induction on the first component then by case analysis on the second component. Here is an example: \begin{coq_eval} -Require Arith. +Require Import Arith. \end{coq_eval} \begin{coq_example} -Infix "<" lt (at level 5, no associativity). -Infix "<=" le (at level 5, no associativity). -Lemma le_or_lt : (n,n0:nat) n0<n \/ n<=n0. -NewInduction n; NewDestruct n0; Auto with arith. -NewDestruct (IHn n0); Auto with arith. +Infix "<" := lt (at level 50, no associativity). +Infix "<=" := le (at level 50, no associativity). +Lemma le_or_lt : forall n n0:nat, n0 < n \/ n <= n0. +induction n; destruct n0; auto with arith. +destruct (IHn n0); auto with arith. \end{coq_example} \question{How to define a function by double recursion?} @@ -539,13 +558,13 @@ NewDestruct (IHn n0); Auto with arith. compilation algorithm to do the work for you. Here is an example: \begin{coq_example} -Fixpoint minus [n:nat] : nat -> nat := - [m:nat]Cases n m of - O _ => O - | (S k) O => (S k) - | (S k) (S l) => (minus k l) - end. -Print minus. +Fixpoint minus (n m:nat) {struct n} : nat := + match n, m with + | O, _ => 0%N + | S k, O => S k + | S k, S l => minus k l + end. +Print minus. \end{coq_example} @@ -558,15 +577,19 @@ the simplest way?} Here is what it gives on e.g. the type of streams on naturals \begin{coq_example} - Set Implicit Arguments. - CoInductive Stream [A : Set] : Set := Cons : A->(Stream A)->(Stream A). - CoFixpoint nats : nat -> (Stream nat) := [n](Cons n (nats (S n))). - - Lemma Stream_unfold : (n:nat)(nats n)= (Cons n (nats (S n))). - Proof. - Intro; Change (nats n) = (Cases (nats n) of (Cons x s) => (Cons x s) end). - Case (nats n); Reflexivity. - Qed. +Set Implicit Arguments. +CoInductive Stream (A:Set) : Set := + Cons : A -> Stream A -> Stream A. +CoFixpoint nats (n:nat) : Stream nat := Cons n (nats (S n)). +Lemma Stream_unfold : + forall n:nat, nats n = Cons n (nats (S n)). +Proof. + intro; + change (nats n = match nats n with + | Cons x s => Cons x s + end). + case (nats n); reflexivity. +Qed. \end{coq_example} \section{Miscellaneous} @@ -600,18 +623,14 @@ Reset Initial. \end{coq_eval} \begin{coq_example*} -Inductive Def1 : Set - := c1 : Def1. - -Inductive DefProp : Def1 -> Set - := c2 : (d:Def1)(DefProp d). - -Inductive Comb : Set - := c3 : (d:Def1)(DefProp d) -> Comb. - -Lemma eq_comb - : (d1,d1':Def1; d2:(DefProp d1); d2':(DefProp d1')) d1=d1' -> - (c3 d1 d2)=(c3 d1' d2'). +Inductive Def1 : Set := c1 : Def1. +Inductive DefProp : Def1 -> Set := + c2 : forall d:Def1, DefProp d. +Inductive Comb : Set := + c3 : forall d:Def1, DefProp d -> Comb. +Lemma eq_comb : + forall (d1 d1':Def1) (d2:DefProp d1) (d2':DefProp d1'), + d1 = d1' -> c3 d1 d2 = c3 d1' d2'. \end{coq_example*} \answer You need to derive the dependent elimination @@ -623,33 +642,30 @@ Abort. \begin{coq_example*} Scheme DefProp_elim := Induction for DefProp Sort Prop. - -Lemma eq_comb - : (d1,d1':Def1)d1=d1'->(d2:(DefProp d1); d2':(DefProp d1')) - (c3 d1 d2)=(c3 d1' d2'). -Intros. -NewDestruct H. -NewDestruct d2 using DefProp_elim. -NewDestruct d2' using DefProp_elim. -Reflexivity. +Lemma eq_comb : + forall d1 d1':Def1, + d1 = d1' -> + forall (d2:DefProp d1) (d2':DefProp d1'), c3 d1 d2 = c3 d1' d2'. +intros. +destruct H. +destruct d2 using DefProp_elim. +destruct d2' using DefProp_elim. +reflexivity. Qed. \end{coq_example*} \question{And what if I want to prove the following?} \begin{coq_example*} -Inductive natProp : nat -> Prop - := p0 : (natProp O) - | pS : (n:nat)(natProp n) -> (natProp (S n)). - -Inductive package : Set - := pack : (n:nat)(natProp n) -> package. - -Lemma eq_pack - : (n,n':nat) - n=n' -> - (np:(natProp n); np':(natProp n')) - (pack n np)=(pack n' np'). +Inductive natProp : nat -> Prop := + | p0 : natProp 0%N + | pS : forall n:nat, natProp n -> natProp (S n). +Inductive package : Set := + pack : forall n:nat, natProp n -> package. +Lemma eq_pack : + forall n n':nat, + n = n' -> + forall (np:natProp n) (np':natProp n'), pack n np = pack n' np'. \end{coq_example*} \answer @@ -659,29 +675,26 @@ Abort. \end{coq_eval} \begin{coq_example*} Scheme natProp_elim := Induction for natProp Sort Prop. - -Definition pack_S : package -> package. -NewDestruct 1. -Apply (pack (S n)). -Apply pS; Assumption. +Definition pack_S : package -> package. +destruct 1. +apply (pack (S n)). +apply pS; assumption. Defined. - -Lemma eq_pack - : (n,n':nat) - n=n' -> - (np:(natProp n); np':(natProp n')) - (pack n np)=(pack n' np'). -Intros n n' Heq np np'. -Generalize Dependent n'. -NewInduction np using natProp_elim. -NewInduction np' using natProp_elim; Intros; Auto. -Discriminate Heq. -NewInduction np' using natProp_elim; Intros; Auto. -Discriminate Heq. -Change (pack_S (pack n np))=(pack_S (pack n0 np')). -Apply (f_equal package). -Apply IHnp. -Auto. +Lemma eq_pack : + forall n n':nat, + n = n' -> + forall (np:natProp n) (np':natProp n'), pack n np = pack n' np'. +intros n n' Heq np np'. +generalize dependent n'. +induction np using natProp_elim. +induction np' using natProp_elim; intros; auto. + discriminate Heq. +induction np' using natProp_elim; intros; auto. + discriminate Heq. +change (pack_S (pack n np) = pack_S (pack n0 np')). +apply (f_equal (A:=package)). +apply IHnp. +auto. Qed. \end{coq_example*} |