一切經音義 94.128

94.128

叵階（上坡我反字統云反可為叵字書云叵謂不可也已見前釋訖）。

Impossible to step up to (叵階: the first character is fanqie po + wo [pǒ]. The Zitong says: "The reversal of kě (可) forms pǒ (叵)." The character dictionaries say: "Po means impossible (bù kě)." Already fully explained above).