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-rw-r--r--_CoqProject1
-rw-r--r--src/Util/IdfunWithAlt.v44
2 files changed, 45 insertions, 0 deletions
diff --git a/_CoqProject b/_CoqProject
index 38f7f99e2..a62bbd701 100644
--- a/_CoqProject
+++ b/_CoqProject
@@ -239,6 +239,7 @@ src/Util/ForLoop.v
src/Util/GlobalSettings.v
src/Util/HList.v
src/Util/HProp.v
+src/Util/IdfunWithAlt.v
src/Util/IffT.v
src/Util/Isomorphism.v
src/Util/IterAssocOp.v
diff --git a/src/Util/IdfunWithAlt.v b/src/Util/IdfunWithAlt.v
new file mode 100644
index 000000000..ed7a82ace
--- /dev/null
+++ b/src/Util/IdfunWithAlt.v
@@ -0,0 +1,44 @@
+(** Some constants that return their first argument, and hold an equal second argument. *)
+Require Import Crypto.Util.Tuple.
+Definition id_with_alt {A} (value : A) (value_for_alt : A) : A
+:= value.
+Definition id_with_alt_proof {A} (value : A) (value_for_alt : A)
+ {pf : value = value_for_alt}
+ : A
+ := id_with_alt value value_for_alt.
+Fixpoint id_tuple'_with_alt {A n}
+ {struct n}
+ : forall (value value_for_alt : tuple' A n),
+ tuple' A n
+ := match n return forall value value_for_alt : tuple' A n, tuple' A n with
+ | O => id_with_alt
+ | S n' => fun (value value_for_alt : tuple' A n' * A)
+ => (@id_tuple'_with_alt A n' (fst value) (fst value_for_alt),
+ @id_with_alt A (snd value) (snd value_for_alt))
+ end.
+Fixpoint id_tuple'_with_alt_proof {A n}
+ {struct n}
+ : forall (value value_for_alt : tuple' A n) {pf : value = value_for_alt},
+ tuple' A n
+ := match n return forall value value_for_alt : tuple' A n, _ -> tuple' A n with
+ | O => id_with_alt_proof
+ | S n' => fun (value value_for_alt : tuple' A n' * A) (pf : value = value_for_alt)
+ => (@id_tuple'_with_alt_proof A n' (fst value) (fst value_for_alt)
+ (f_equal (@fst _ _) pf),
+ @id_with_alt_proof A (snd value) (snd value_for_alt)
+ (f_equal (@snd _ _) pf))
+ end.
+Definition id_tuple_with_alt {A n}
+ : forall (value value_for_alt : tuple A n), tuple A n
+ := match n with
+ | O => id_with_alt
+ | S n' => id_tuple'_with_alt
+ end.
+Fixpoint id_tuple_with_alt_proof {A n}
+ {struct n}
+ : forall (value value_for_alt : tuple A n) {pf : value = value_for_alt},
+ tuple A n
+ := match n with
+ | O => id_with_alt_proof
+ | S n' => id_tuple'_with_alt_proof
+ end.