Goal:
  
  __x3 : Z
  __x2 : Z
  __x1 : Z
  __wit := [] : list ZMicromega.ZArithProof
  __varmap := VarMap.Branch (VarMap.Elt __x2) __x1 (VarMap.Elt __x3)
           : VarMap.t Z
  __ff := Tauto.A Tauto.isProp
            {|
              RingMicromega.Flhs :=
                EnvRing.PEadd (EnvRing.PEX 1)
                  (EnvRing.PEadd (EnvRing.PEX 2) (EnvRing.PEX 3));
              RingMicromega.Fop := RingMicromega.OpEq;
              RingMicromega.Frhs :=
                EnvRing.PEadd (EnvRing.PEadd (EnvRing.PEX 1) (EnvRing.PEX 2))
                  (EnvRing.PEX 3)
            |} tt : Tauto.BFormula (RingMicromega.Formula Z) Tauto.isProp
  ============================
   (__x1 + (__x2 + __x3) = __x1 + __x2 + __x3)


DEBUG:Going to execute:
exact
(ZMicromega.ZTautoChecker_sound __ff __wit
   (eq_refl <: ZMicromega.ZTautoChecker __ff __wit = true)
   (VarMap.find 0 __varmap))