“…For a quantum network of three nodes, the density operator ρ( j, k, l) is given by Refs. [13], [20], [21], and [22], for brevity we will not list this expression, here we only point out that equation ( 4) can be directly obtained from ρ( j, k, l) by emptying the first node j, hereafter we shall use the symbols j, k, l to represent the quantities related to the first, the second, and the third nodes respectively, hence the density operators corresponding to three degenerated two-nodes quantum states ρ(k, l), ρ( j, l), ρ( j, k) can be directly obtained from ρ( j, k, l) by emptying j, k, l respectively. Equation ( 4) can be written as [13,17,20,21] ρ(k, l) = ρ(k) ⊗ ρ(l)…”