Manduka Karika:- Sage Gaudapada wrote or compiled the Manduka Karika, also known as the Sage Gaudapada Karika.+

Manduka Karika:- Sage Gaudapada wrote or compiled the Manduka Karika, also known as the Sage  Gaudapada Karika and as the Agama Śāstra. 

The Manduka Karika is a commentary in verse form on the Manduka Upanishad, one of the shortest but most profound Upanishads, or mystical Vedas, consisting of just 13 prose sentences. 

In Sage Sankara’s time, it was considered to be a Sruti, but not particularly important. In later periods it acquired a higher status, and eventually, it was regarded as expressing the essence of the Upanishad philosophy.

The Manduka Karika is the earliest extant systematic treatise on Advaita Vedanta, though it is not the oldest work to present Advaita views, nor the only pre-Sankara work with the same type of teachings.

Sage Gaudapada took over the Buddhist doctrines that "that the nature of the world is the four-cornered negation”. Sage Gaudapada "wove [both doctrines] into a philosophy of the Manduka Upanishad, which was further developed by Sage Sankara.":~Santthosh Kumaar