Goal:
  
  G1 : t
  ext : EdgeSet.t
  f : EdgeSet.elt -> VSet.t -> VSet.t
  trf : transpose VSet.Equal f
  prpf : Proper (eq ==> VSet.Equal ==> VSet.Equal) f
  x : EdgeSet.elt
  i : VSet.t
  ============================
   (VSet.Equal (f x i) (f x i))


DEBUG:Going to execute:
solve
[ do
![ solve
 [ trivial | apply : eq_sym ; trivial ]
 | discriminate
 | contradiction
 | Ltac.split ]
| case not_locked_false_eq_true; Ltac.assumption
| match goal with
  | H:~ _ |- _ => solve [ case H; trivial ]
  end ]