From 4b075af747f65bcd73ff1c78417cf77edf6fbd76 Mon Sep 17 00:00:00 2001
From: Hugo Herbelin
Date: Thu, 21 Jan 2016 01:13:56 +0100
Subject: Fixing some problems with double induction.

Basically, the hypotheses were treated in an incorrect order, with a
hack for sometimes put them again in the right order, resulting in
failures and redundant hypotheses.

Status unclear, because this new version is incompatible except in
simple cases like a double induction on two "nat".

Fixing the bug incidentally simplify the code, relying on the
deprecation since 8.4 to allow not to ensure a compatibility (beyond
the simple situation of a double induction on simple datatypes).

See file induct.v for effect of changes.
---
 test-suite/success/induct.v | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

(limited to 'test-suite')

diff --git a/test-suite/success/induct.v b/test-suite/success/induct.v
index 7ae60d9892..9413b8dae9 100644
--- a/test-suite/success/induct.v
+++ b/test-suite/success/induct.v
@@ -151,3 +151,46 @@ intros x H1 H.
 induction H.
 change (0 = z -> True) in IHrepr''.
 Abort.
+
+(* Test double induction *)
+
+(* This was failing in 8.5 and before because of a bug in the order of
+   hypotheses *)
+
+Inductive I2 : Type :=
+  C2 : forall x:nat, x=x -> I2.
+Goal forall a b:I2, a = b.
+double induction a b.
+Abort.
+
+(* This was leaving useless hypotheses in 8.5 and before because of
+   the same bug. This is a change of compatibility. *)
+
+Inductive I3 : Prop :=
+  C3 : forall x:nat, x=x -> I3.
+Goal forall a b:I3, a = b.
+double induction a b.
+Fail clear H. (* H should have been erased *)
+Abort.
+
+(* This one had quantification in reverse order in 8.5 and before *)
+(* This is a change of compatibility. *)
+
+Goal forall m n, le m n -> le n m -> n=m.
+intros m n. double induction 1 2.
+3:destruct 1. (* Should be "S m0 <= m0" *)
+Abort.
+
+(* Idem *)
+
+Goal forall m n p q, le m n -> le p q -> n+p=m+q.
+intros *. double induction 1 2.
+3:clear H2. (* H2 should have been erased *)
+Abort.
+
+(* This is unchanged *)
+
+Goal forall m n:nat, n=m.
+double induction m n.
+Abort.
+
-- 
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