The affix denoting denoting 'who studies or who knows that' is elided by luk after the title of a sūtra work having k as penultimate.,
Thus अष्टकं is the title of Panini sutra. Those who study अष्टकं and will be called also अष्टकः, as अष्टकाः पाणिनीयाः 'those who study, the Ashtaka'. So also दशका वैयाघ्रपदीयाः, त्रिकाः काशकृत्स्नाः ॥
Vart:- The elision takes place only where the title is formed by a numeral: as in the examples above given. Thus महावार्तिकं सूत्रमधीते = महावार्तिकः, so also कालापकः ॥
Why do we say \having क् for its penultimate\? Observe चतुष्टयमधीते = चातुष्टयः ॥ This sutra applies, of course, to those words which are not formed by affixes denoting प्रोक्त or the Announcer.,