def _has_true(self, e, extra_constraints=(), solver=None, model_callback=None): 
raise BackendError("<STR_LIT>")<EOL>
The native version of :func:`has_true`.

:param e:                   The backend object.
:param extra_constraints:   Extra constraints (as ASTs) to add to the solver for this solve.
:param solver:              A solver, for backends that require it.
:param model_callback:      a function that will be executed with recovered models (if any)
:return:                   A boolean.