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+(** Bug #2281
+
+In the code below, coq is confused by an equality unless it is first 'subst'ed
+away, yet http://coq.inria.fr/stdlib/Coq.FSets.FSetDecide.html says
+
+    fsetdec will first perform any necessary zeta and beta reductions and will
+invoke subst to eliminate any Coq equalities between finite sets or their
+elements.
+
+I have coq r12851.
+
+*)
+
+Require Import Arith.
+Require Import FSets.
+Require Import FSetWeakList.
+
+Module DecidableNat.
+Definition t := nat.
+Definition eq := @eq nat.
+Definition eq_refl := @refl_equal nat.
+Definition eq_sym := @sym_eq nat.
+Definition eq_trans := @trans_eq nat.
+Definition eq_dec := eq_nat_dec.
+End DecidableNat.
+
+Module NatSet := Make(DecidableNat).
+
+Module Export NameSetDec := WDecide (NatSet).
+
+Lemma ThisLemmaWorks : forall ( s1 s2 : NatSet.t )
+                              ( H : s1 = s2 ),
+                       NatSet.Equal s1 s2.
+Proof.
+intros.
+subst.
+fsetdec.
+Qed.
+
+Import FSetDecideAuxiliary.
+
+Lemma ThisLemmaWasFailing : forall ( s1 s2 : NatSet.t )
+                              ( H : s1 = s2 ),
+                       NatSet.Equal s1 s2.
+Proof.
+intros.
+fsetdec.
+(* Error: Tactic failure: because the goal is beyond the scope of this tactic.
+*)
+Qed.
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