Quantum hamiltonian reduction refers to a collection of functors that map the module category of a given affine vertex algebra to those of its associated W-algebras. Some of these functors are reasonably well understood and then the representation theory of the W-algebra is accessible. But some are not. Inverse quantum hamiltonian reduction is a recent discovery that there (sometimes) exist functors in the opposite direction: from a given W-algebra module category to that of another W-algebra, which may be the affine vertex algebra itself. I will give an overview of the simplest example, which connects the module categories of the Virasoro and sl2 minimal model vertex operator algebras.
