Non-convex polyhedra
The five regular and the 13 semi-regular polyhedra can be transformed into non-convex structures.
a. The original rhombicuboctahedron with 18 squares and 8 triangles
b. Ibidem with twelve of the 18 squares non-convex
c. Ibidem with six of the 18 squares and 8 of the 8 triangles non-convex