Goal:
  
  G : t
  HI : invariants G
  HG : acyclic_no_loop G
  y_0 : V.t
  x_0 : V.t
  Vx : VSet.In x_0 (V G)
  Vy : VSet.In y_0 (V G)
  K : Z
  Hxs : lsp G x_0 y_0 = Some K
  S : VSet.t
  u : V.t
  v : V.t
  q : SPath G' S u v
  ============================
   match from_G' q with
   | inl q' => sweight q = sweight q'
   | inr (q1, q2) => sweight q <= sweight q1 - K + sweight q2
   end


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