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 eq... https://foldlyers.shop/product-category/screws/