Yoga Sūtra Chapter Three verse 7

trayam-antar-aṅgaṃ pūrvebhyaḥ ||7||

The three are the internal limb from the preceding.

traya - the threeantar - internalaṅga - limbpūrva - preceding

Commentaries and Reflections

TKV Desikachar:

Pūrva Aṅga is essentially a process of elimination
in which we eliminate those thoughts that are not relevant.
In fact Yoga is the process of eliminating the undesirable
so we can be linked with the desirable.
It is the movement from Saṃyoga to Viyoga,
from Saguṇa to Nirguṇa.
But we must be careful how we define desirable or undesirable.”
TKV Desikachar Madras December 19th 1988