JÃ nos Bolyai ( December 15 , 1802 â `` January 27 , 1860 ) was a Hungarian mathematician , known for his work in non-Euclidean geometry . JÃ nos Bolyai ( pronounced ) ( December 15 , 1802 â `` January 27 , 1860 ) was a Hungarian mathematician , known for his work in non-Euclidean geometry .