Goal:
    G : t  s0 : VSet.t  x : V.t  u : VSet.elt  Hu : u = x
  ============================
   (sweight (split (spath_refl s0 x) u (right Hu)).1 +
    sweight (split (spath_refl s0 x) u (right Hu)).2 =
    sweight (spath_refl s0 x))


DEBUG:Going to execute:
destruct Hu