Unavoidable set of face types for planar maps

@article{Hork1996UnavoidableSO,
  title={Unavoidable set of face types for planar maps},
  author={Mirko Horň{\'a}k and Stanislav Jendrol’},
  journal={Discuss. Math. Graph Theory},
  year={1996},
  volume={16},
  pages={123-141}
}
The type of a face f of a planar map is a sequence of degrees of vertices of f as they are encountered when traversing the boundary of f . A set T of face types is found such that in any normal planar map there is a face with type from T . The set T has four infinite series of types as, in a certain sense, the minimum possible number. An analogous result is applied to obtain new upper bounds for the cyclic chromatic number of 3-connected planar maps. 

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