2-regular graph

Set

 context $V,E$ … set
 definiendum $\langle V,E,\psi\rangle \in \mathrm{it}(E,V)$
 inclusion $\langle V,E,\psi\rangle$ … undirected graph
 for all $v\in V$
 postulate $d(v)=2$

Discussion

A finite 2-regular graph consists disconnected cycles.

A general 2-regular graph consists disconnected cycles or infinite chains.