Goal:
  
  G : t
  s : VSet.t
  s' : VSet.t
  x : V.t
  y : V.t
  n : Z
  Hn : lsp0 s x y = Some n
  Hs : VSet.Subset s s'
  ============================
   (Some n <= lsp0 s' x y)%nbar


DEBUG:Going to execute:
apply lsp0_spec_eq in Hn; destruct Hn as [p Hp]