Māheśvarasūtrāni or pratyāhārasūtrāṇi are 14 in number. First sutra is aiuṇ. It is described in the Pratyāhārāhnika of Mahābhāṣya written by Pataῆjali.  The first vārtika in this sutra is, akārasya vivṛtopadeśa ākāragrahaṇārthaḥ.  Here is a short description on this Vartika.

पतञ्जलेः व्याकरणमहाभाष्यस्य द्वितीयम् आह्निकं भवति प्रत्याहाराह्निकम्।  तत्र अइउण् इति प्रथमं प्रत्याहारसूत्रम्।  तत्रापि प्रथमं वार्तिकं भवति-अकारस्य विवृतोपदेश आकारग्रहणार्थः।  तस्य वार्तिकस्य व्याख्यानं भवत्यत्र।

Yatharthanubhava (यथार्थानुभवः) is of four types, pratyaksa, anumana, upamana, and sabda.

Pratyksa is divided into two, nirvikalpaka and savikalpaka.

Anumana is divided into two, svartha and parartha. (अनुमानं द्विविधम्-स्वार्थं परार्थं च)

Evolution of Prakrt Languages and different prakrts.

The concept of Buddhi according to Tarkasangraha.

Buddhi is divided into two; Smrti and Anubhava.

Some differences between Vedic Sanskrit and Classical Sanskrit.

Vedic Sanskrit and Classical Sanskrit.

Genealogical Classification of languages, Different families of languages.

Indo-European family of languages and its 10 divisions.

Morphological Classification of languages-agglutinating languages-prefix agglutination, suffix agglutination, prefix-suffix agglutination-Inflectional languages.

Morphological Classification

Isolating languages

Agglutinating languages