Goal:
  
  G1 : t
  G2 : t
  sub : subgraph G1 G2
  acG2 : acyclic_no_loop G2
  x : V.t
  p : PathOf G1 x x
  ============================
   (?y <= 0)


DEBUG:Going to execute:
<coq-core.plugins.ssreflect::ssrapply@0> $1