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 Image](https://www.idlehearts.com/images/proofs-of-the-euclidean-parallel-postulate-can-be-developed-to-such-an.jpg?x85372 "Proofs of the Euclidean [parallel] postulate can be developed to such an")
