S Rule
When a vowel other than "a", a "k" or "r" precedes "s", s changes into ṣ.
Example:
- karo + si ⇒ karoṣi
- gaccha + si ⇒ gacchasi (remains in front because of "a")
- deve + su ⇒ deveṣu
- bhavat + su ⇒ bhavatsu (remains in front because of "t")
N Rule
When ṣa, ra, ṛ, or ṝ precedes n, n turns into ṇ which gutturals, labials and "y" potentially in between.
Examples:
- rāma + ena ⇒ rāmeṇa
- rat + ena ⇒ ratena (remains insertion because of dental "t")
- kārya + ena ⇒ kāryeṇa
- viṣaya + ānām ⇒ viṣayāṇām
- bheṣaja + ānām ⇒ bheṣajānām (remains insertion because of palatal "j")