Let $m,n,p,q$ be \reftext{def:natural-numbers-2026a}{natural numbers}. Let $A$ be an $m\times n$ real matrix, let $B$ be an $n\times p$ real matrix, and let $C$ be a $p\times q$ real matrix, with all products taken in the sense of \reftext{def:product-real-matrices-2026a}{the matrix product definition}. Then