From 6ae29940af487e03ef2eafc9cb5c9b0d015c6a7c Mon Sep 17 00:00:00 2001
From: Hugo Herbelin
Date: Sun, 15 Nov 2020 13:28:41 +0100
Subject: Fixes #12348: long-standing de Bruijn indices bug in imitation
 (solve_simple_eqn).

The bug was that an assumption could be interpreted as a local
definition and wrongly expanded.

It triggered rarely because it involved mixing let-ins and
local assumptions + imitation under binders.
---
 pretyping/evarsolve.ml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

(limited to 'pretyping')

diff --git a/pretyping/evarsolve.ml b/pretyping/evarsolve.ml
index de41c8f22f..c58ebe1bbd 100644
--- a/pretyping/evarsolve.ml
+++ b/pretyping/evarsolve.ml
@@ -1576,7 +1576,7 @@ let rec invert_definition unify flags choose imitate_defs
     match EConstr.kind !evdref t with
     | Rel i when i>k ->
         let open Context.Rel.Declaration in
-        (match Environ.lookup_rel (i-k) env' with
+        (match Environ.lookup_rel i env' with
         | LocalAssum _ -> project_variable (RelAlias (i-k))
         | LocalDef (_,b,_) ->
           try project_variable (RelAlias (i-k))
-- 
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