四分律刪繁補闕行事鈔 3.409

3.409

若界中人少，對首作法，一同眾法對首；無人者，同眾法心念。

If there are few people within the boundary, performing the ritual face-to-face is entirely identical to the face-to-face communal proceedings; if there is no other person, it is identical to the mental resolve of the communal proceedings.