Perfect and Imperfect Ground Forms

Let 0(nP s ) denote a circular single coronoid as in Chapt. 5. Furthermore, introduce 

GP(rio as a ground form obtained by a two-contact addition of a hexagon to O. Then the formula coefficients obey 

DefinUioiis 6.S (a) A perfect ground form (of single coronoids), G, is a single coronoid with the 

The spiral walk generates exactly one G system (G or G ) for every possible formula (tIq 5q). It should be observed, however, that there may be several nonisomorphic systems G Uq 5q for a given formula, and it may happen that some of them have not the structure of a hexagon added to a circular coronoid. 

The associated benzenoid to G is a ground form benzenoid, while the associated 

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