शीङो रुट्

The अत् substitute of झ gets the रुट् augment after the root शी।
Thus शेरते, शेरताम्, अशेरत ॥ The augment र् is added at the beginning of the affix, making अत् = रत् ॥ Had this र् been an augment of झ, then like the आट् augment in शयान्तै, it would have intervened between the शी and झ, and झ not immediately following a non-अ stem, अत् would not have been substituted for झ at all. Therefore रुट् is made the augment of the substitute अत, and not of झ ॥ The root शी is read in the sutra with its anubandha ङ् in order to indicate, that there is no रुट् augment when there is elision of the Intensive affix यङ्, nor any Guna. As व्यति शेश्यते ॥

It is a general rule that an operation applying to a root which is exhibited with an anubandha, will not apply to the same root in its Intensive-yan-luk form. The following verse shows when operations applying to simple roots will not apply to their Intensive forms:--

श्तिपा शपानुबन्धेन निर्दिष्टं यद्गणेन च ।
यत्रैकाज् ग्रहणं चैव पंचैतानि न यङ्लुकि ॥

"These five sorts of operations will not apply to Intensive-yan-luk forms: 1. When the simple root is exhibited in the sutra with श्तिप् as भू in 7.4.73 is shown as भवति ॥ In Intensive, the perfect will be बोभवाञ्चकार and not बभवाञ्चकार ॥ 2. Where the root is exhibited with शप्, as the root भृ in 7.2.49 is shown as भर ॥ There is इट् after the Desiderative of simple root but not in Intensive. 3. When a simple root is exhibited with an anubhandha, as शीङ् here. 4. Where a gana is mentioned in a rule, as श्यन् is taught after Divadi-roots 3.1.69. It will apply to simple roots of Divadi gana, and not to their Intensive. 5. Lastly, where the word एकाच् is used in a sutra. As 7.2.10. That rule will apply to एकाच् simple roots and not to their Intensives.