शि तुक्

Thus भवाञ् च्छेते ॥ The augment is added to the end of the preceding word, and not to the beginning of the second word, in order to change श into छ ॥ In fact, the augment धुट् added to the second would have been as good as तुक्, namely both are त; but then छ change would not have taken place.

Objection:- If this be so, then why न् is not changed to ण्, since it is no longer final in a pada, when तुक् is added to it, in कुर्वञ् च्छेते ॥

Answer:- This is to be thus explained. The sutra स्तोः श्चुना श्चुः 8.4.40 should be divided into two parts, in order to prevent ण change. Thus the first part will be स्तोः श्चुना, which will mean that स and तु followed by श and चु will not cause the change of न to ण ॥ The next sutra will be श्चुः, which will mean that the preceding स and तु are changed to श and चु respectively.,