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author | letouzey <letouzey@85f007b7-540e-0410-9357-904b9bb8a0f7> | 2006-04-25 22:52:18 +0000 |
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committer | letouzey <letouzey@85f007b7-540e-0410-9357-904b9bb8a0f7> | 2006-04-25 22:52:18 +0000 |
commit | b2e0ec34cdd95017ce9ecec99b3431494b452d6c (patch) | |
tree | ccbc1c35da20152063cc5d094cc2e1b256fa4cf0 /theories/Arith/Div2.v | |
parent | 0274e797162cd62fe9145436a66027a61d727d64 (diff) |
Un gros coup de lifting pour IntMap:
* le type ad des adresses est maintenant un alias vers
le N de NArith, qui lui est isomorphe.
* toutes les operations sur ces adresses (p.ex. un xor
bit a bit) sont maintenant dans de nouveaux fichiers du
repertoire NArith.
* Intmap utilise maintenant le meme type option que le
reste du monde
* etc etc...
Tout ceci ne preserve pas forcement la compatibilite. Les 4 contribs
utilisant Intmap sont adaptees en consequence. Me demander si besoin
ma moulinette d'adaptation (incomplete).
git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@8733 85f007b7-540e-0410-9357-904b9bb8a0f7
Diffstat (limited to 'theories/Arith/Div2.v')
-rw-r--r-- | theories/Arith/Div2.v | 22 |
1 files changed, 22 insertions, 0 deletions
diff --git a/theories/Arith/Div2.v b/theories/Arith/Div2.v index 16a832e27..bfa767f57 100644 --- a/theories/Arith/Div2.v +++ b/theories/Arith/Div2.v @@ -173,3 +173,25 @@ Lemma odd_S2n : forall n, odd n -> {p : nat | n = S (double p)}. Proof. intros n H. exists (div2 n). auto with arith. Qed. + +(** Doubling before dividing by two brings back to the initial number. *) + +Lemma div2_double : forall n:nat, div2 (2*n) = n. +Proof. + induction n. + simpl; auto. + simpl. + replace (n+S(n+0)) with (S (2*n)). + f_equal; auto. + simpl; auto with arith. +Qed. + +Lemma div2_double_plus_one : forall n:nat, div2 (S (2*n)) = n. +Proof. + induction n. + simpl; auto. + simpl. + replace (n+S(n+0)) with (S (2*n)). + f_equal; auto. + simpl; auto with arith. +Qed. |