'Return a constant :class:`.False_` construct.
E.g.::
>>> from sqlalchemy import false
>>> print select([t.c.x]).where(false())
SELECT x FROM t WHERE false
A backend which does not support true/false constants will render as
an expression against 1 or 0::
>>> print select([t.c.x]).where(false())
SELECT x FROM t WHERE 0 = 1
The :func:`.true` and :func:`.false` constants also feature
"short circuit" operation within an :func:`.and_` or :func:`.or_`
conjunction::
>>> print select([t.c.x]).where(or_(t.c.x > 5, true()))
SELECT x FROM t WHERE true
>>> print select([t.c.x]).where(and_(t.c.x > 5, false()))
SELECT x FROM t WHERE false
.. versionchanged:: 0.9 :func:`.true` and :func:`.false` feature
better integrated behavior within conjunctions and on dialects
that don\'t support true/false constants.
.. seealso::
:func:`.true`'

@classmethod
def _singleton(cls):

    return FALSE
