Goal:
  
  s : VSet.t
  s' : VSet.t
  x : V.t
  y : V.t
  H : DisjointAdd x s s'
  H' : x <> y
  y0 : VSet.elt
  ============================
   (VSet.In y0 (VSet.remove y s') -> x = y0 \/ VSet.In y0 (VSet.remove y s))


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

Not an inductive goal with 1 constructor.
Level 0: Backtrace:

Not an inductive goal with 1 constructor.