पक्षात् तिः

The word मूल of the last sutra is drawn into this aphorism; and not the word पाक as well. This is an exceptional case of अनुवृत्ति, generally the whole is drawn and not a portion. Hence arises the following maxim क्वचिदेकदेशोऽप्यनुवर्तते \Sometimes it also happens that only a part of the words of a rule which are mutually connected is valid in a subsequent rule, while the rest ceases to be valid\.

Thus पक्षस्य मूलं = पक्षतिः i. e. प्रतिपत् 'the root or the first day of a Paksha or a fortnight'.,