Possibilities of Circumscribing and Excising

Excising. Any single or multiple coronoid C (as well as any benzenoid) can be excised. 

The degenerate coronoid system exds—C2 where C2 is the j polyhex (double coronoid) of Fig. 3.1 excis-C72H26 = C36H20. 

It should not be suppressed, however, that an excised coronoid very often is another (smaller) coronoid. In particular, every time a coronoid can be circumscribed so that 

Circumscribing, The situation for drcumscribing coronoids (as well as benzenoids) is quite different from that of exdsing the systems. 

Assume that a coronoid C can be drcumscribed as is manifested by eqn. (9). Then is determined unambiguously for the given C. Also conversely if is given, then C may be 

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