Example  DOM.L.2.  Suppose $h(x)=log_2(3−x)$. Visualize the domain of $h$ on a graph and a mapping diagram.
Solution: The domain of the function $h$ is visualized both on the graph and the mapping diagram by a green open ended ray on the "$X$-axis".

Comment: Here we consider $g(x) = 3-x$ and the domain is $\{x : 3-x >0\} = (-\infty, 3)$.