Goal:
  
  G : t
  HI : invariants
  z : V.t
  hin : VSet.In z (V G)
  x : V.t
  y : V.t
  x0 : Z
  ine : VSet.In (x, x0, y)..s (V G) /\ VSet.In (x, x0, y)..t (V G)
  p : PathOf y z
  IHp : VSet.In z (V G) -> VSet.In y (V G)
  ============================
   (VSet.In x (V G))


DEBUG:Going to execute:
contradiction
Level 1: Backtrace:

 The relation VSet.In is not a declared symmetric relation. Maybe you need to require the Coq.Classes.RelationClasses library
Level 0: Backtrace:

 The relation VSet.In is not a declared symmetric relation. Maybe you need to require the Coq.Classes.RelationClasses library
Level 0: Backtrace:

 The relation VSet.In is not a declared symmetric relation. Maybe you need to require the Coq.Classes.RelationClasses library