Goal:
    _z_ : VSet.t  x0 : V.t  x1 : V.t  x2 : V.t  x3 : V.t  a : V.t  H : x1 = a
  ============================
   (x2 = a)


DEBUG:Going to execute:
<Coq.Init.Tauto.is_empty> flags X1; elim H
Level 4: Backtrace:

In environment
_z_ : VSet.t
x0, x1, x2, x3, a : V.t
H : x1 = a
Unable to unify "a" with "x2".
Level 4: Backtrace:

In environment
_z_ : VSet.t
x0, x1, x2, x3, a : V.t
H : x1 = a
Unable to unify "a" with "x2".
Level 5: Backtrace:

In environment
_z_ : VSet.t
x0, x1, x2, x3, a : V.t
H : x1 = a
Unable to unify "a" with "x2".
Level 5: Backtrace:

In environment
_z_ : VSet.t
x0, x1, x2, x3, a : V.t
H : x1 = a
Unable to unify "a" with "x2".
Level 4: Backtrace:

In environment
_z_ : VSet.t
x0, x1, x2, x3, a : V.t
H : x1 = a
Unable to unify "a" with "x2".
Level 4: Backtrace:

In environment
_z_ : VSet.t
x0, x1, x2, x3, a : V.t
H : x1 = a
Unable to unify "a" with "x2".