Antonio Leon demonstrated Euclid's 5th postulate.

[Laurence Clark Crossen]

Antonio Leon
"New Elements of Euclidean Geometry" Revised 2023
"Apparent Relativity" Revised 2023
Both books available free at Academia.edu

He demonstrates Euclid's 5th postulate, something supposedly ridiculous to claim, since many attempted to do this for over 2,000 years without success.

The non-Euclidean geometries take as a pretext the alleged inability to prove the 5th postulate to embark on their unproven claims.

Jeremiah Joseph Callahan already accomplished the same in his 1931 book, "Euclid or Einstein: A Proof of the Parallel Theory and a Critique of Metageometry"