Goal:
  
  G : t
  HI : invariants G
  HG : acyclic_no_loop G
  n : Z
  x : V.t
  y : V.t
  Vy : ~ VSet.In y (V G)
  Hle : leq_vertices G n x y
  nneg : n <= 0
  n0 : x <> y
  Hxs : lsp G x (s G) = None
  Vx : VSet.In x (V G)
  n1 : x <> s G
  ============================
   (x <> s G)


DEBUG:Going to execute:
done
Level 1: Backtrace:

Proof is not complete.
Level 1: Backtrace:

Proof is not complete.
Level 1: Backtrace:

Proof is not complete.
Level 1: Backtrace:

Proof is not complete.
Level 1: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No matching clauses for match.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.
Level 1: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.