Past exam of the mathematics course of the University of Cambridge / 2021 / ib / Paper 2 / 2F / a / Solution

Let $\Vert K{\Vert }_{\infty }={\max }_{[0,1{]}^2}|K|$. For $f,g\in C([0,1])$,Taking the supremum over $x$ proves that the integral operator $T$ is Lipschitz continuous, hence continuous, in the uniform norm.

It remains to see that $Tf$ is continuous. Since $K$ is uniformly continuous on the compact square and $f$ is bounded,as $x^{\prime }\to x$. Therefore $T:C([0,1])\to C([0,1])$ is well defined and continuous.