sathya viveka suthra sthavah - sanskrit
పితృస్మృతి - Pithru smruthi - sanskrit - ఆచార్య సంతోష్ కుమార్
Eight Insightful Upanishads with Sanskrit Verses Listing
Kathopnishad Maithili with Original Sanskrit text and introduction in English
Eight Insightful Upanishads with Sanskrit Verses Listing