Solution
= Solution
Taking the <trace> of the proposed <commutator> identity would give
$$
0=\operatorname{tr}(AB)-\operatorname{tr}(BA)=\operatorname{tr}I=n,
$$
a contradiction for positive integer $n$ over the real numbers. \b[No such finite real matrices exist.] This is the <trace of a commutator> obstruction; it also applies to complex finite matrices.