only holds in good cases. In this paper, we show that categorically, the duality between joins
and intersections holds in the framework of homological projective duality (HPD)[K07], as
long as the intersections have expected dimensions. This result together with its various
applications provide further evidences for the proposal of homological projective geometry
of Kuznetsov and Perry [KP18]. When the varieties are inside disjoint linear subspaces, our …