# ARIATIONS OF CONCAVE PYRAMIDS OF SECOND SORT WITH AN EVEN NUMBER OF BASE SIDES

## Authors

• Slobodan Misic University of Belgrade
• Branislav Popkonstantinovic University of Belgrade

## Keywords:

concave polyhedron, concave pyramid, deltahedral lateral surface, regular polygonal basis

## Abstract

Concave pyramids of second sort (CP II) are formed similarly to concave cupolae of second sort (CC II) with a comparable logic of emergence to the regular-faced convex pyramids. They are formed by enclosing the space over a regular polygonal base by the lateral deltahedral wrapper consisting of equilateral triangles meeting in common apex. The plane net is composed of double row of equilateral triangles, so it is possible to form a regular faced pyramid even with bases greater than pentagonal, whereat the obtained polyhedron will be concave. In this paper we focus on a type of concave pyramids of second sort formed over the basic polygons with an even number of sides, type CP II-B which has half the number of lateral unit cells than the type CP II-A.

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