Question -
Answer -
Let A and B be two non-empty sets. A relation from A to B, i.e., a subset of A├ЧB, is called a function (or a mapping) from A to B, if
(i) for each a тИИ A there exists b тИИ B such that (a, b) тИИ f
(ii) (a, b) тИИ f and (a, c) тИИ f тЗТ b = c