Graph-theoretically nonplanar

It remains to treat graph-theoretically nonplanar polyhexes. We shall not attempt to give any systematic classification of the variety of these systems, but present some examples in the next section. 

Here the left-hand system is graph—theoretically nonplanar like the systems of Figs. 6 and 7. However, the right-hand isomer is a graph—theoretically planar system and actually a corohelicene similar to the system of Fig. 4. 

Definition 2.5 A corohelicene (system) is a multiply connected, geometrically nonplanar (helicenic) polyhex, which is graph-theoretically planar. 

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