The 6th-Case-affix is not used when the word is governed by a verbal noun in aka denoting futurity, or in a in denoting 'futurity and indebtedness'.,
The affix अक, such as ण्वुल, वुञ् &c., denote futurity, and never denote indebtedness. The affix इन् such as णिनि 3.3.3 and 3.3.170 denotes both. Thus कटं कारको व्रजति 'he goes to make a mat.' ओदनं भोजको व्रजति 'he goes to eat rice.' So also with इन्, as ग्रामंगमी or ग्रामी 'he has to go to the village.' शतं दायी 'he owes hundred.'
Why do we say 'when denoting futurity or indebtedness' ? Observe यवानां लावकः 'the cutter of barley.' सक्तूनां पावकः, अवश्यं करी कटस्य ॥
Why is the Genitive employed in the following वर्षशतस्य पूरकः, पुत्रपौत्राणां दर्शकः ? The words पूरक and दर्शक, though formed by अक 3.1.133, are not formed by that अक which denotes futurity, viz., (II . 3. 10). The present sutra relates to this latter अक, and not every अक in general.,