  Let $f \in M_+(\mathbb{R}_+)$, the class of nonnegative, Lebesgure-measurable
functions on $\mathbb{R}_+=(0, \infty)$. We deal with integral operators of the
form \[ (T_Kf)(x)=\int_{\mathbb{R}_+}K(x,y)f(y)\, dy, \quad x \in \mathbb{R}_+,
\] with $K \in M_+(\mathbb{R}_+^2)$.
