妙法蓮華經玄贊 5.156

5.156

贊曰：舉他明自作佛生喜。佛記他作佛，彰我亦得作，故知佛道實叵思議，方便隨宜令我解了。「叵」者不可也。「反」正為乏，反可為叵，皆字意故。

Eulogy: Citing others to elucidate one's own attainment of Buddhahood and arouse joy. The Buddha prophesying that another will become a Buddha clarifies that I also may become one; thus we know that the Buddha path is truly inconceivable, and through expedient means suited to circumstances he brings us to understanding. Po (叵) means 'cannot' (不可). Reversing zheng (正) makes fa (乏), and reversing ke (可) makes po (叵); both derive from the structural composition of the characters.