Goal:
    x : V.t  y : V.t  p : VSet.t  H : x <> y  a : V.t
  ============================
   ((x = a \/ VSet.In a p /\ y <> a -> (x = a \/ VSet.In a p) /\ y <> a) /\
    ((x = a \/ VSet.In a p) /\ y <> a -> x = a \/ VSet.In a p /\ y <> a))


DEBUG:Going to execute:
repeat
            match goal with
            | H:context [ ?x <> ?y ]
              |- _ => assert new (x = y \/ x <> y) by
              apply VSetDecide.MSetDecideAuxiliary.dec_eq
            | H:context [ ~ VSet.In ?x ?s ]
              |- _ => assert new (VSet.In x s \/ ~ VSet.In x s) by
              apply VSetDecide.MSetDecideAuxiliary.dec_In
            | |- context [ ?x <> ?y ] => assert new 
              (x = y \/ x <> y) by
              apply VSetDecide.MSetDecideAuxiliary.dec_eq
            | |- context [ ~ VSet.In ?x ?s ] => assert new
              (VSet.In x s \/ ~ VSet.In x s) by
              apply VSetDecide.MSetDecideAuxiliary.dec_In
            end