Saccheri–Legendre theorem

The Saccheri-Legendre theorem is a result in non-Euclidean geometry, specifically related to the study of parallel lines and the nature of space in different geometric contexts. The theorem is named after the Italian mathematician Giovanni Saccheri and the French mathematician Adrien-Marie Legendre. ### Statement of the Theorem: The theorem revolves around the properties of quadrilaterals that have two equal sides perpendicular to the base, known as Saccheri quadrilaterals.