Definition: Admitted polygonal objects in this paper

Faces are embedded flat polygonal disks in spacelike affine planes. They need not be convex. The fixed exterior may contain unbounded polygonal faces. Regular vertices need not be trivalent.

At a singular event parameter, collapsed cells are not positive dimensional cells of the slice. Their labels and one-sided formulas may be retained as germ metadata. A change between two such labelled germs is an admissible event when the two germs have the same underlying limiting slice and the prescribed common exterior.