俱舍論疏 17.79

17.79

論「一俱轉者至得一支遠離」，明一俱轉。此是有人不能具受五戒等，但發願期心唯不殺等。正起業時，惡、無記心現在前，故唯有一。

The passage of the śāstra from "When one operates simultaneously" up to "one obtains the abstention of a single branch" explains the simultaneous operation of one. This refers to someone who is unable to fully receive the five precepts, etc., but merely makes a vow and sets their mind only on not killing, etc. When directly initiating the action, an unwholesome or indeterminate mind is currently present, and therefore there is only one.