# Is {(1, 2); (1, 3); (1, 4); (1, 5)} a function?

To be a function the same value of $x$ can not map into multiple values of $y$
Since $\left(x , y\right) = \left\{\begin{matrix}1 & 2 \\ 1 & 3 \\ 1 & 4 \\ 1 & 5\end{matrix}\right\}$
has $x$ (as $1$) mapping into 4 different values,