俱舍論疏 18.131

18.131

論「若有六因至非最輕重」，明三結也。六上最重、六下最輕，隨闕少多，非極上下。

Regarding the Śāstra's "If possessed of the six causes..." down to "...neither the most light nor the most heavy": this explains the three conclusions. Being highest in the six causes is the heaviest; being lowest in the six is the lightest; depending on whether more or fewer are lacking, it is not the extreme upper or lower.