Goal:
  
  G1 : t
  G2 : t
  H : invariants G1
  H0 : invariants G2
  H1 : acyclic_no_loop G2
  sub : subgraph G1 G2
  ext : is_true (is_full_extension G1 G2)
  v1 : VSet.elt
  v2 : VSet.elt
  H2 : VSet.In v1 (V G1)
  H3 : VSet.In v2 (V G1)
  ============================
   (lsp G2 v1 v2 <= lsp G1 v1 v2)%nbar


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 ]