I love Tom Lehrer, but I was a little taken aback when I learnt that Lobachevsky was a real mathematician and not as far as anyone knows a plagiarist. Seems harsh to skewer a (long-dead) guy's reputation with such a catchy song.
It's the one occasion I can think of where I feel Tom Lehrer's satire was truly misdirected. One of many reasons I appreciate him so much is otherwise that when the sharp wit was at someone's expense, they had earned it (and this in contrast to the practice with most contemporary purported comedians, at least in my country).
http://www.claymath.org/euclid/index/book-1-postulates (the image is clickable, but it's all greek to me)
https://en.wikipedia.org/wiki/Parallel_postulate#History
I think Lehrer was counting on both the Danny Kaye reference and his prosody statement to hint at where this song stands with respect to Poe's Law: https://news.ycombinator.com/item?id=24281288