Links
[1] https://www.hootsgo.org/?q=node/6554
[2] https://bineeshthomas.wordpress.com/2011/05/24/sutra-3-urdhva-tiryagbhyam-sutra-multiplication-of-two-integers-adyamadyenantyamantyena/
[3] https://liberius1776.wordpress.com/tag/urdhva-tiryagbhyam/
[4] http://vedicmathematics.blogspot.co.uk/2007/12/urdhva-tiryagbhyam.html