In recent work with T. Dimofte and D. Gaiotto, we explained how to construct 2d N=(0,2) interfaces between two 3d N=2 IR-dual theories. These duality interfaces are codimension-one defects that implement the map of operators across the duality. After reviewing this construction, we will explain a geometric correspondence, inherited from the 6d N=(2, 0) theory, that associates such an interface to a 4-simplex with boundary. As a simple starting point towards exploring triangulated 4-manifolds with field theoretic techniques, we translate a basic geometric operation on a 4-simplex into an IR equivalence of duality interfaces. Based on work to appear with T. Dimofte.