In the fifteenth century Rāmachandra, in his Prakriyā-kaumudī, or "Moonlight of Method," endeavoured to make Pāṇini's grammar easier by a more practi… - Panini

The Pāṇinian commentator Kātyāyana (c. 3rd–4th century BCE) knew of the coexistence of Middle Indic forms with earlier ones. There is a Pāṇinian rule that provides that verb bases listed in an appendix to the Aṣṭādhyāyī have the class name dhātu (verbal base, root). Kātyāyana discusses whether one could define verbal bases semantically and thereby possibly do without the verb list. He remarks that even if one defines a verbal base as denoting an action, the roots must be listed in order to preclude the possibility that constituents of terms such as āṇapayati/āṇavayati ‘commands’ be assigned the class name in question; āṇapayati/āṇavayati is a Middle Indic counterpart of Sanskrit ājñāpayati.

Pingala was the brother of Panini.

The current language Pāṇini describes is very close in structure to the late Vedic found in certain Brāhmaṇa texts. As noted earlier, scholars have recognized other varieties of Sanskrit. Epic Sanskrit is so called because it is represented principally in the two epics, Mahābhārata (“Great Epic of the Bhārata Dynasty”) and Rāmāyaṇa (“Romance of Rāma”). In the latter the term saṃskṛta ‘adorned, cultivated, purified (by grammar)’ is encountered, possibly for the first time with reference to the language. The date of composition for the core of early Epic Sanskrit is considered to be in the centuries just preceding the Common Era.