Figure 2.

The eight allowed ‘nets’ enclosing up to two internal helices [see (17) for a detailed description of nets]. Single strands s₀, s₁, etc. are stretched by internal helices whose apparent lengths l₁ and l₂ depend on the ‘entanglement state’ of each helix, see main text. Conformational entropy parameters for all allowed nets and an example of transition barrier (see Supplementary Material 2) are given in Table 1.