Our illustration (plate 5) shows a 45-45-90-degree triangle with squares-or what looks like squares-built on its sides and on the hypotenuse. But wait! Something seems to be going on: 5^2+5^2=7^2, or 25+25=49! Did anything go wrong? Do we see here an optical illusion? Not really: the Pythagorean theorem, not the theorem itself; as such it is not bound by the laws of mathematics. To quote the American artist Josef Albers (1888-1976): "In science, one plus one is always two; in art it can also be three or more.