Possible Duplicate:
Tetrahedral torus
Assume now, i have many regular tetrahedral of the same size and i would stick one to another face to face. Is it possible to form a cycle like a ring, i.e. sticking the last tetrahedral to one introduce at the very begining and forming a cycle?
What i have thought is that i know the position of vertex of a new tetrahedral when sticking it on the face of the previous one, it just like reflection, and i can find it by matrices easily.