From 7f25b156d2e33ec767732175f7030cd103e9b695 Mon Sep 17 00:00:00 2001
From: Georges Gonthier
Date: Mon, 18 Mar 2019 12:49:18 +0100
Subject: remove dependency on hidden case branch types

Anticipating coq/coq#9170, remove numeric occurrence selector affected
by the (invisible) presence of explicit types for variables bound in
`match` branch patterns. The proof could be further simplified if this
change is implemented.
---
 mathcomp/ssreflect/fintype.v | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

(limited to 'mathcomp')

diff --git a/mathcomp/ssreflect/fintype.v b/mathcomp/ssreflect/fintype.v
index 2544ab6..93810ca 100644
--- a/mathcomp/ssreflect/fintype.v
+++ b/mathcomp/ssreflect/fintype.v
@@ -1950,8 +1950,12 @@ Variant split_spec m n (i : 'I_(m + n)) : 'I_m + 'I_n -> bool -> Type :=
 
 Lemma splitP m n (i : 'I_(m + n)) : split_spec i (split i) (i < m).
 Proof.
-rewrite /split {-3}/leq.
-by case: (@ltnP i m) => cmp_i_m //=; constructor; rewrite ?subnKC.
+(* We need to prevent the case on ltnP from rewriting the hidden constructor  *)
+(* argument types of the match branches exposed by unfolding split. If the    *)
+(* match representation is changed to omit these then this proof could reduce *)
+(* to by rewrite /split; case: ltnP; [left | right. rewrite subnKC].          *)
+set lt_i_m := i < m; rewrite /split.
+by case: {-}_ lt_i_m / ltnP; [left | right; rewrite subnKC].
 Qed.
 
 Definition unsplit {m n} (jk : 'I_m + 'I_n) :=
-- 
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