Originally Posted by

**atrain313131** Sorry about that - this is how it is written in the book:

"Two functions are equal if they have the same domain, the same codomain, and "agree" on every element of the domain. More formally,

Theorem: If f: A -> B and g: A -> B are functions, then f=g if and only if f(a) = g(a) for all a that are an element of A.

(Hint: a function is a relation. Saying that two functions are equal is to say they are relations between the same pair of sets, and they include the same ordered pairs.)"