Eves, Howard (2012), Foundations and Fundamental Concepts of Mathematics, Courier Dover Publications, стр. 59, ISBN9780486132204, „We also owe to Lambert the first systematic development of the theory of hyperbolic functions and, indeed, our present notation for these functions.”
Ratcliffe, John (2006), Foundations of Hyperbolic Manifolds, Graduate Texts in Mathematics, 149, Springer, стр. 99, ISBN9780387331973, „That the area of a hyperbolic triangle is proportional to its angle defect first appeared in Lambert's monograph Theorie der Parallellinien, which was published posthumously in 1786.”
