Ramakrishna Paramahamsa went into Nirvikalpa Samadhi within 3 days! He did not need to study Upanishads etc! praNAms Hare Krishna I think it is shankara bhagavatpAda who said 4 chapters in mAndUkya is the essence of sarva upanishat-s. Sri Subbu prabhuji any help?? Hari Hari Hari bol!!! bhaskar