Three Spherical Triangles of Equal Area
This Demonstration shows three spherical triangles. Triangles and have a common base and the same area, so they are equivalent by dissection (as shown in Dissection of Two Spherical Triangles with a Common Base). Triangles and also have a common base and the same area, so they are also equivalent by dissection. So triangles and are equivalent by dissection.[more]
Therefore, spherical triangles with the same area are equivalent by dissection.[less]
 P. Gerwien, "Zerschneidung jeder beliebigen Anzahl von gleichen geradlinigen Figuren in dieselben Stücke," Journal für die reine und angewandte Mathematik (Crelle's Journal), 10, 1833 pp. 228–234, and Taf. 3. gdz.sub.uni-goettingen.de/dms/load/img/?PID=GDZPPN002139170.
 Wikipedia. "Saccheri Quadrilateral." (Mar 20, 2017) en.wikipedia.org/wiki/Saccheri_quadrilateral.