From ab initio random structure search combined with DFT investigations of the ground state properties Mujica et al. proposed body center tetragonal (BCT) tetragonal C . The structure is documented in the carbon allotropes database SACADA with No. 66 and the topology "4/5/t1". Such a topology analyzer is readily available online with the 'TopCryst' program . Fig. shows the C 16 structure with space group I4 1 /a, No. 88, in ball-and-stick and polyhedral representations of C at 16f: 0.0986, 0.34645, 0.02958) with a tet = 4.474 Å, and c tet =4.500 Å. By considering the structure in a lower symmetry BCT space group I4 1 No. 80, the 16 atoms become dispatched over two Wyckoff positions at (8b) with 0.0986, 0.34645, 0.02958 as above, and a second 8b' with 0.34645,0.901400, 0.97042 and the same lattice constants as above. The structure, with two similar carbon substructures, is shown in Fig. in two different colors of spheres. We then noticed that the removal of one of the two substructures leads to C 8 (Fig. ) featuring a trigonal carbon structure as shown on the righthand-side RHS polyhedral projection. The structure was found with srs topology (SACADA No.5 ) representing trigonal carbon in a 3D crystal build, i.e., versus G planar trigonal carbon in G2D approach, as discussed above. Consequently, the interconnections of the two trigonal-like carbon substructures lead to the tetrahedral structure as shown in this example.