Goal:
  
  s : VSet.t
  s' : VSet.t
  s'' : VSet.t
  da : forall a : V.t, VSet.In a s -> VSet.In a s'
  i : V.t
  disj : VSet.In i (VSet.inter s' s'') -> False
  ininter : VSet.In i (VSet.inter s s'')
  H : VSet.In i s -> VSet.In i s'
  ============================
   (VSet.In i (VSet.inter s' s''))


DEBUG:Going to execute:
repeat match goal with
                  | H:forall a : V.t, _ |- _ => clear H
                  end
Level 3: Backtrace:

Tactic failure (level 1).
Level 2: Backtrace:

Tactic failure.
Level 2: Backtrace:

Tactic failure.
Level 3: Backtrace:

Tactic failure.
Level 2: Backtrace:

Tactic failure.
Level 1: Backtrace:

No matching clauses for match.