Goal:
  
  x : V.t
  p : VSet.t
  a : V.t
  H : x = a \/ x = a \/ VSet.In a p
  H0 : x = a
  ============================
   (x = a \/ VSet.In a p)


DEBUG:Going to execute:
<coq-core.plugins.ltac::clear@0> $1