Why is diamond 1 mole of carbon and 2 moles of carbon-carbon bond in the crystal structure?

The crystal structure of diamond is a spatial network structure. Each carbon atom and four surrounding carbon atoms form a regular tetrahedron, that is, a carbon atom in the center of the regular tetrahedron participates in the formation of four C-C single bonds, and its "contribution" to a C-C single bond is 1/2. Therefore, the number of C-C single bonds formed by this carbon atom at the center of the regular tetrahedron is equivalent to 4× 1/2.