What is the fine-grained topic of the following text: It mentions first an ascetic Purushôttama-mahâtîrtha, who is represented to have been an incarnation of the god Vishṇu (v. 1) and to have composed a commentary (v. 2) which is not known from other sources. Only return the topic.
Purushôttama-mahâtîrtha's incarnation as Vishṇu and his unknown commentary