„Do not try the parallels in that way: I know that way all along. I have measured that bottomless night, and all the light and all the joy of my life went out there.“
— Farkas Bolyai
Letter to János Bolyai (4 April 1820)<!--Marosvásárhely, 1820. április 4.--> Published in: Samu Benkő (ed.), Bólyai-levelek, Kriterion, 1975, p. 123<!--http://hps.elte.hu/courses/tudtort/bolyai.pdf PDF page 2--> As quoted in: O'Connor, John J.; Robertson, Edmund F., "Farkas Bolyai" http://www-groups.dcs.st-and.ac.uk/history/Biographies/Bolyai_Farkas.html, MacTutor History of Mathematics archive, University of St Andrews. Having himself spent a lifetime unsuccessfully trying to prove Euclid's fifth postulate, Farkas discouraged his son János from any further attempt.