Sheldon Axler著『Linear Algebra Done Right Fourth Edition』

行列の積が結合法則を満たすこと、すなわち

(A * B) * C = A * (B * C)

が成り立つことを証明せよという問題に対してAxlerさんは以下のようにコメントしています：

Try to find a clean proof that illustrates the following quote from Emil Artin:
"It is my experience that proofs involving matrices can be shortened by 50% if one throws the matrices out."