Fig. 2: Self-penetrating nets and the QG.
From: Determining dimensionalities and multiplicities of crystal nets

The crystal structures of Cu2O (a) and Ag(B(CN)4) (b). c The net with multiplicity of 2 shown in a 2 × 2 × 2 supercell. d The QG of Cu2O. The disconnected networks are colored in red and blue, respectively.