def _check_graph(obj: _mo.MathObject) -> bool:
"""Return ``True`` if ``obj`` is (almost) a :term:`graph`. Perform all checks except for the
membership in the :term:`algebra of clans`."""
return isinstance(obj, _mo.Set) and obj.get_left_set() == _mo.Set('s', 'p', 'o') \
and obj.is_left_regular()
