Horatio Scott Carslaw, [The elements of non-Euclidean plane geometry and trigonometry (1916)][1] Duncan M'Laren Young Sommerville [The elements of non-Euclidean geometry (1919)][2] [1]: http://archive.org/details/elementsofnoneuc00carsuoft [2]: http://archive.org/details/elementsofnoneuc00sommuoft