Definition 2. Let \(A\) and \(B\) be sets. A map is a set \(\varphi \subseteq\) \(A \times B\) such that for each \(a \in A\) there is exactly one \(b \in B\) with \(\left( a, b \right) \in \varphi\).
Definition 2. Let \(A\) and \(B\) be sets. A map is a set \(\varphi \subseteq\) \(A \times B\) such that for each \(a \in A\) there is exactly one \(b \in B\) with \(\left( a, b \right) \in \varphi\).