Harrumph. Response to the math quiz in my February diary was not up to the

usual standard. Sharpen up your pencils, please — yes! you there in the

back row, and get rid of that gum please. I see I shall have to start

giving pop quizzes.

What is interesting about that function’s derivative is that though it has a

supremum and an infimum in any open interval containing zero, it never

manages to attain either!

The supremum and infimum are 24 and minus 24, respectively.

(Math teachers note: I got that from one of my old textbooks, Gelbaum and

Olmsted’s Counterexamples in Analysis (1964), a goldmine for this sort of

thing.)