Goal:
    x : V.t  s : VSet.t
  ============================
   (~ VSet.In x (VSet.remove x 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.