Coerces a Bool, None, or int into Bit/Propositional form

def coerce(value):
        """
        Coerces a Bool, None, or int into Bit/Propositional form
        """
        if isinstance(value, BoolCell):
            return value
        elif isinstance(value, Cell):
            raise CellConstructionFailure("Cannot convert %s to BoolCell" % \
                    type(value))
        elif value in [1, T]:
            return BoolCell(T)
        elif value in [0, -1, F]:
            return BoolCell(F)
        elif value in [None, U]:
            return BoolCell(U)
        else:
            raise CoercionFailure("Don't know how to coerce %d to Bool" % \
                    (value))