I have a question about a step in the proof of 5.3.17 in Liu's "Algebraic Geometry" (page 201):
My question is why does Prop. 3.1.24 imply that
$$\mathcal{O}_{SpecB} \cong q_*\mathcal{O}_{X_B}$$
hold? Is it a consequence of the projection formula? Which role play the assumption that $q$ is projective? Does it fulfill a special case of projection formula?