Goal:
  
  G1 : t
  G2 : t
  embed : subgraph G1 G2
  x : V.t
  y : V.t
  w : Z
  ine : EdgeSet.In (x, w, y) (E G1)
  ============================
   (EdgeOf G2 x y)


DEBUG:Going to execute:
<coq-core.plugins.ltac::exists@1> $1