Goal:
  
  G : t
  z : V.t
  x : V.t
  y : V.t
  z0 : V.t
  e : EdgeOf x y
  p : PathOf y z0
  q : PathOf z0 z
  IHp : weight (concat p q) = weight p + weight q
  ============================
   (e.π1 + weight (concat p q) = e.π1 + weight p + weight q)


DEBUG:Going to execute:
auto with core arith zarith bool datatypes crelations relations