@classmethod
def _from_base_layout(cls, layout, added_sig=[1, -1], **kw
    ) ->'ConformalLayout':
    """ helper to implement :func:`clifford.conformalize` """
    sig_c = list(layout.sig) + added_sig
    return cls._from_sig(sig=sig_c, firstIdx=layout.firstIdx, layout=layout,
        **kw)
