Music: A Mathematical Offering

A really good book about maths and music by David J. Benson, available as a free pdf, or in a more old fashioned form.

'In real life, as in group theory, operations seldom satisfy the commutative law. For example, if we put on our socks and then put on our shoes, we get a very different effect from doing it the other way round. The associative law is much more commonly satisfied'.

pg325.