Counterexample

Demo note. This note demonstrates what the SciDraft Hugo theme can do for academic and scientific publishing — for research institutions, researchers and students. Its content is demonstration material only: readers should ignore whether the demo content is correct. A counterexample is the cheapest way to kill a plausible statement, and the one worth having ready concerns the order of matrix multiplication. The tempting assertion that \(AB = BA\) fails for almost every pair of matrices, and it fails on the smallest possible example. ...

Demo note. This note demonstrates what the SciDraft Hugo theme can do for academic and scientific publishing — for research institutions, researchers and students. Its content is demonstration material only: readers should ignore whether the demo content is correct. Convexity is often described as the property that guarantees a unique optimum, and the statement is false as written: convex functions can have a whole interval of minimisers. The counterexample is a flat-bottomed function, convex everywhere and constant on a segment. ...