When contempt is to be expressed, the affix cha (as well as the affix ṭhak) comes in the sense of descendant after a prātipadika (Nominal Stem) ending in the affix phiñ and denoting a sauvīra gotra,
Karika
यमुन्दश्च सुयामा च वार्ष्यायणिः फिञः स्मृताः ।
सौवीरेषु च कुत्सायां द्वौ योगौ शब्दवित् स्मरेत् ॥
Thus the son of यमुन्द will be यामुन्दायनिः formed by the affix फिञ् 4.1.154 as this word belongs to Tikadi class. The son of Yamundayani will be either यमुन्दायनीयः or यामुन्दायनिकः ॥
But when contempt is not to be expressed, the son of यामुन्दायनिः will be यामुन्दायनिः ॥ Thus यामुन्दायनि + अण् = यामुन्दायनि + o (Il. 4. 58) = यामुन्दायनिः ॥
So also when persons of Suvira country are not meant, छ is not added. Thus तैकायनिः ॥
The फेः of the sutra refers to फिञ् and not to फिन्, for a stem formed by फिन् will not have a Vriddhi letter in the first syllable and will not be called 'Vriddham'; and the anuvritti of this word is understood in the sutra.
According to the Karika, three फिञन्त stems, all belonging to Tikadi class, are only governed by this sutra viz यमुन्द, सुयामा and वार्ष्यायणिः ॥ The son of वृष is Varshyayani.,