Answer the following question: Given the following passage  "Later Indian materialist Jayaraashi Bhatta (6th century) in his work Tattvopaplavasimha ("The upsetting of all principles") refuted the Nyaya Sutra epistemology. The materialistic Cārvāka philosophy appears to have died out some time after 1400. When Madhavacharya compiled Sarva-darśana-samgraha (a digest of all philosophies) in the 14th century, he had no Cārvāka/Lokāyata text to quote from, or even refer to.",  answer the following question. Note that the answer is present within the text.  Question: What writings were unavailable for research to Madhavacharya?
Answer:
Cārvāka/Lokāyata text