def _torf(args):
    """Return True if all args are True, False if they
    are all False, else None.

    >>> from sympy.core.logic import _torf
    >>> _torf((True, True))
    True
    >>> _torf((False, False))
    False
    >>> _torf((True, False))
    """
    sawT = sawF = False
    for a in args:
        if a is True:
            if sawF:
                return
            sawT = True
        elif a is False:
            if sawT:
                return
            sawF = True
        else:
            return
    return sawT
