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'')
  ininter : VSet.In i (VSet.inter s s'')
  ============================
   (VSet.In i (VSet.inter s' s''))


DEBUG:Going to execute:
progress change T with V.t in H;
            repeat
             match goal with
             | J:_ |- _ => progress change T with V.t in J
             | |- _ => progress change T with V.t
             end
DEBUG LTAC Evaluated term: V.t
DEBUG LTAC Evaluated term: V.t
Level 1: Backtrace:

Failed to progress.
Level 1: Backtrace:

Failed to progress.
Level 1: Backtrace:

Failed to progress.