Thinking Mathematically (6th Edition)

$\{x|0\leq x\leq4\}$
From the graph we can see that intimacy is greater than commitment in years $0$ to $4$. So let $x$ be the years. Then a good inequality is $0\leq x\leq4$. This in set builder notation is: $\{x|0\leq x\leq4\}$