I'm with David here. For some purposes it is genuinely useful to know that all categorical concepts can be reduced to "terminal object", or that the entire theory of deterministic computation can be emulated within group theory. But that doesn't mean that this should always be done! Mathematics is all about knowing many ways to look at something, and choosing the right one(s). "Knowledge is knowing that a tomato is a fruit. Wisdom is not putting it into a fruit salad." Best to all, Robert Dawson ---------- You're receiving this message because you're a member of the Categories mailing list group from Macquarie University. Leave group: https://outlook.office365.com/owa/categories@mq.edu.au/groupsubscription.ashx?source=EscalatedMessage&action=leave&GuestId=6bf90c14-94d1-45b7-a0b5-9dd447734d27