wallis was also inspired by the works of islamic mathematician sadr al-tusi, the son of nasir al-din al-tusi, particularly by al-tusi's book written in 1298 on the parallel postulate. the book was based on his father's thoughts which presented one of the earliest arguments for a non-euclidean hypothesis equivalent to the parallel postulate. after reading this, wallis then wrote about his ideas as he developed his own thoughts about the postulate, trying to prove it also with similar triangles.