chapter  XV
Criticism of Euclid's Postulate V: Non-Euclidean Geometries
Pages 35

To the mathematicians who came after Euclid, his fifth postulate seemed less obvious than the rest. This led to efforts to demonstrate it from the other postulates and axioms, taking as a basis the first 28 propositions of Book I of the Elements, in which, as we have said, the famous postulate is not used.