Science absolute of space, independent of the truth or falsity of Euclid's axiom XI (which can never be decided a priori) / by John Bolyai ; translated [from the appendix contributed by J. Bolyai to F. Bolyai's "Tentamen juventutem studiosam in elementa
The Secret treaties and understandings : text of the available documents / with introductory comments and explanatory notes by F. Seymour Cocks and a preface by Charles Trevelyan.