大比丘三千威儀 1.9

1.9

六者，不知二制。或有戒二三因緣合為一戒，或有因緣二開乃至六開，是名不知二制。

Sixth, not understanding dual promulgations: where a precept combines two or three causes and conditions into a single precept, or has causes and conditions allowing exemptions twice up to six times—this is called not understanding dual promulgations.