Goal:
    x : V.t  s : VSet.t  y : V.t  H0 : x = y -> False  H1 : VSet.In y s
  ============================
   (x = y)


DEBUG:Going to execute:
match goal with
           | |- _ -> _ => intro; t_tauto_intuit
           | |- _ => t_reduce; t_solver
           end