Link to source

Petit, J.P. (1982), Os Mistérios da Geometria, col. "As Aventuras de Anselmo Curioso", Publicações Dom Quixote, Lisboa

MARANER, P. (2010), A Spherical Pythagorean Theorem, in "THE MATHEMATICAL INTELLIGENCER", Springer Science+Business Media, p. 46

Link to source

Desargues, Girard (1639), Brouillon :project: projet d'une Atteinte aux :evenemens, événements, des rencontres du cone avec un plan , par L,S,G,D,L.

Dickinson, W., Salmassi, M. (2008), The Right Right Triangle on the Sphere, The College Mathematics Journal, Vol. 39, No. 1 (Jan., 2008), pp. 24-33

Link to source

Ward, John (1758), Young Mathematician's Guide, 10th Ed, Hitch&Hawes, London.

I Lénárt, Comparative Geometry in Distance Education