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


DEBUG:Going to execute:
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