Proofs of the Euclidean [parallel] postulate can be developed to such an extent that apparently a mere trifle remains. But a careful analysis shows that in this seeming trifle lies the crux of the matter; usually it contains either the proposition that is being proved or a postulate equivalent to it.
![Proofs of the Euclidean [parallel] postulate can be developed to such an extent that apparently a mere trifle remains. But a careful analysis shows that in this seeming trifle lies the crux of the matter; usually it](http://cdn.quoteddaily.com/images/johann-heinrich-lambert/proofs-of-the-euclidean-parallel-postulate-can-be-developed-to-such-an-extent-that-apparently-a-mere-trifle-remains-but.jpg)