Goal:
    s' : VSet.t  t0 : VSet.t  a : V.t  H : VSet.In a s'
  ============================
   (VSet.In a t0 \/ VSet.In a s')


DEBUG:Going to execute:
repeat match goal with
                  | _:~ ?P, H:?P \/ ~ ?P |- _ => clear H
                  end
Level 1: Backtrace:

No matching clauses for match.