Goal:
  
  x : V.t
  s1 : VSet.t
  s2 : VSet.t
  addx : VSetProp.Add x s1 s2
  xnotins1 : ~ VSet.In x s1
  y : VSet.elt
  ============================
   (VSet.In y (VSet.add x s2) <-> x = y \/ VSet.In y s1)


DEBUG:Going to execute:
case not_locked_false_eq_true; Ltac.assumption
Level 1: Backtrace:

Not an inductive definition.
Level 0: Backtrace:

Not an inductive definition.
Level 1: Backtrace:

Proof is not complete.
Level 0: Backtrace:

Proof is not complete.
Level 0: Backtrace:

Proof is not complete.
Level 0: Backtrace:

Proof is not complete.