From 14e47506ffabc43c25bf8da108abb6df78b803ad Mon Sep 17 00:00:00 2001
From: Hugo Herbelin
Date: Thu, 29 Sep 2016 17:33:47 +0200
Subject: Being more informative about the change of behavior of "subst".

---
 CHANGES       | 5 ++++-
 COMPATIBILITY | 6 ++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/CHANGES b/CHANGES
index c3eaae6ee0..cf1fefa75d 100644
--- a/CHANGES
+++ b/CHANGES
@@ -27,7 +27,10 @@ Specification language
 Tactics
 
 - Flag "Bracketing Last Introduction Pattern" is now on by default.
-- Flag "Regular Subst Tactic" is now on by default.
+- Flag "Regular Subst Tactic" is now on by default: it respects the
+  initial order of hypothesis, it contracts cycles, it unfolds no
+  local definitions (common source of incompatibilities, fixable by
+  "Unset Regular Subst Tactic").
 - New flag "Refolding Reduction", now disabled by default, which turns
   on refolding of constants/fixpoints (as in cbn) during the reductions
   done during type inference and tactic retyping. Can be extremely
diff --git a/COMPATIBILITY b/COMPATIBILITY
index 892eaa599e..d423e71df3 100644
--- a/COMPATIBILITY
+++ b/COMPATIBILITY
@@ -11,6 +11,12 @@ Remedy:
   instead (compatible with 8.4).
 - Unset the option for the program/proof the obligation/subproof originates
   from.
+
+Symptom: In a goal, order of hypotheses, or absence of an equality of
+the form "x = t" or "t = x", or no unfolding of a local definition.
+Cause: This might be connected to a number of fixes in the tactic
+"subst". The former behavior can be reactivated by issuing "Unset
+Regular Subst Tactic".
   
 Potential sources of incompatibilities between Coq V8.4 and V8.5
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