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


DEBUG:Going to execute:
t_solver
Level 4: Backtrace:

Failed to progress.
Level 4: Backtrace:

Failed to progress.
Level 4: Backtrace:

Failed to progress.
Level 5: Backtrace:

Failed to progress.
Level 4: Backtrace:

Failed to progress.
Level 4: Backtrace:

Failed to progress.
Level 4: Backtrace:

Failed to progress.
Level 4: Backtrace:

Failed to progress.
Level 4: Backtrace:

Failed to progress.
Level 3: Backtrace:

Failed to progress.