Imported Upstream snapshot 8.3~beta0+13298

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+(* Bug #2137
+
+The fsetdec tactic is sensitive to which way round the arguments to <> are.
+In the small, self-contained example below, it is able to solve the goal
+if it knows that "b <> a", but not if it knows that "a <> b". I would expect
+it to be able to solve hte goal in either case.
+
+I have coq r12238.
+
+
+Thanks
+Ian
+
+*)
+
+Require Import Arith FSets 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 ( s0 : NatSet.t )
+                              ( a b : nat ),
+                       b <> a
+                    -> ~(NatSet.In a s0)
+                    -> ~(NatSet.In a (NatSet.add b s0)).
+Proof.
+intros.
+fsetdec.
+Qed.
+
+Lemma ThisLemmaWasFailing : forall ( s0 : NatSet.t )
+                              ( a b : nat ),
+                       a <> b
+                    -> ~(NatSet.In a s0)
+                    -> ~(NatSet.In a (NatSet.add b s0)).
+Proof.
+intros.
+fsetdec.
+(*
+Error: Tactic failure: because the goal is beyond the scope of this tactic.
+*)
+Qed.
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