docs: def unsat_core(self, extra_constraints=()):
          """
          This function returns the unsat core from the backend solver.
  
          :param extra_constraints:   Extra constraints (as ASTs) to add to the solver for this solve.
          :return: The unsat core.
          """
          if o.CONSTRAINT_TRACKING_IN_SOLVER not in self.state.options:
              raise SimSolverOptionError('CONSTRAINT_TRACKING_IN_SOLVER must be enabled before calling unsat_core().')
          return self._solver.unsat_core(extra_constraints=extra_constraints)