Dijsktra Making Good Sense
And if you have not a ready-made function [...] at your disposal in terms of which to describe the net effect of such a compound statement, invent this function and be sure that its properties are nice and also the ones that you want. If you cannot find such a function, don’t ignore that warning, for then you are on the verge of messing things up.
EWD-273 by Edsger Dijkstra.
(Perhaps I’m going to turn this weblog into my commonplace book, though I do want to get back to the backlog of book reviews...)