Goal:
  
  s : VSet.t
  s' : VSet.t
  s'' : VSet.t
  x : V.t
  hadd : VSetProp.Add x s s'
  hin : ~ VSet.In x s
  H : ~ VSet.In x s''
  ============================
   (~ VSet.In x (VSet.union s s''))


DEBUG:Going to execute:
VSetDecide.MSetDecideAuxiliary.abstract_term t
Level 1: Backtrace:

Tactic failure: no need to abstract a variable.
Level 2: Backtrace:

Tactic failure: no need to abstract a variable.
Level 2: Backtrace:

Tactic failure: no need to abstract a variable.
Level 1: Backtrace:

Tactic failure: no need to abstract a variable.
Level 2: Backtrace:

Tactic failure: no need to abstract a variable.
Level 2: Backtrace:

Tactic failure: no need to abstract a variable.
Level 1: Backtrace:

Tactic failure: no need to abstract a variable.