the stilted and indeed fallacious demonstration of Euclid forsakes us at the why, and a simple figure, which we already know, and which is present to us, gives at a glance far more insight into the matter, and firm inner conviction of that necessity, and of the dependence of that quality upon the right angle: -
kateto desberdinen kasuan ere horrelako konbikzio begiesgarri batera eramanak izatea onartu beharra daukagu, oro har edozein egia geometriko ahalgarritan bezala;