On the theorem of Pythagoras by by E.W. Dijkstra. (Did you know that in every plane triangle sgn$(\alpha + \beta - \gamma)$ = sgn$(a^2 + b^2 - c^2)$, a "theorem, say, 4 times as rich [as the original]"?)

On the theorem of Pythagoras by E.W. Dijkstra. (Did you know that in every plane triangle $\operatorname{sgn}(\alpha + \beta - \gamma) = \operatorname{sgn}(a^2 + b^2 - c^2)$, a "theorem, say, 4 times as rich [as the original]"?)