It " contains formulae for right-handed triangles, the general law of sines, and the solution of a spherical triangle by means of the polar triangle . " This treatise later had a " strong influence on European mathematics ", and his " definition of ratios as numbers " and " method of solving a spherical triangle when all sides are unknown " are likely to have influenced Regiomontanus.
32.
I haven't given this article the thorough attention it deserves, but one passage caught my attention : " He also discovered a result similar to Snell's law of sines, but did not quantify it and derive the law mathematically . " One of the two sources he cited, an educational article on use of historical examples in the teaching of optics, cites a reprint of David Lindberg's " The Cause of Refraction in Medieval Optics " as saying Alhazen's theory was " suspiciously Cartesian . " ( p 28 ) Unfortunately, this tertiary source missed Lindberg's footnote ( p . 29, n . 23 ) where he questioned the Cartesian interpretation of Alhazen.
