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


DEBUG:Going to execute:
fun id0 id1 X2 => assert X2; [ exact (id0 id1) | clear id0 ]