The generalized Iitaka conjecture for klt pairs

Let $(X,B)$ be a projective klt pair with $B$ a $Q$-boundary, and let $f\colon X\to Z$ be an algebraic fibre space onto a smooth projective variety $Z$. Let $F$ be a general fibre of $f$, and define

$$K_F+B_F:=(K_X+B)|_F.$$

Generalized Iitaka conjecture. One has

$$\kappa(K_X+B)\geq \kappa(K_F+B_F)+\kappa(Z).$$

This is a generalized form of the Iitaka conjecture for the Kodaira dimension of a log pair, extending the expected subadditivity inequality from varieties to klt pairs. The source presents it after proving a special case for bases of maximal Albanese dimension; its general validity is not established here.