Stan's Tetrahedron

This puzzle was invented in the 1980's, probably by Leonard Gordon. Stan Isaacs told me he remembers finding the interlocking solution for this puzzle and it has become associated with his name. It is usually made from spheres, here I made it out of rhombic dodecahedra. There are two pieces (red in the photos) plus two more which are mirror images (yellow).

The pieces can be assembled into an order 4 tetrahedron in two ways. One solution interlocks quite well, you can hold it upside down a