Pullbacks of hyperplane sections for Lagrangian fibrations are primitive

Let [Formula: see text] be a Lagrangian fibration on a hyperkähler manifold of maximal holonomy (also known as IHS), and [Formula: see text] be the generator of the Picard group of [Formula: see text]. Assume that [Formula: see text] has no multiple fibers in codimension 1. We prove that [Formula: see text] is a primitive class on [Formula: see text].