def _an_element_(self):
"""
Try to return an element of ``self``, as per
:meth:`Sets.ParentMethods.an_element`.
For each parent ``self`` is a facade for, this default
implementation tries the method ``an_element`` until it finds an
element in ``self``. If none is found raise a
``NotImplementedError``.
EXAMPLES::
sage: S = Sets().Facades().example(); S
An example of facade set: the monoid of positive integers
sage: S.an_element()
1
"""
for parent in self.facade_for():
x = parent.an_element()
if x in self:
return x
raise NotImplementedError
def _an_element_(self):
"""
Try to return an element of ``self``, as per
:meth:`Sets.ParentMethods.an_element`.
For each parent ``self`` is a facade for, this default
implementation tries the method ``an_element`` until it finds an
element in ``self``. If none is found raise a
``NotImplementedError``.
EXAMPLES::
sage: S = Sets().Facade().example(); S
An example of facade set: the monoid of positive integers
sage: S.an_element()
1
"""
for parent in self.facade_for():
x = parent.an_element()
if x in self:
return x
raise NotImplementedError