Published online by Cambridge University Press: 03 November 2016
For convenience we shall repeat here the definition by Hawkins, Hill, Reeve and Tyrrell (1, hereafter referred to as HHRT) of a k-map:
Definition
A map is called a k-map if each of the following conditions is satisfied:
(i) It is a map on a sphere;
(ii) Each face is a connected region whose boundary is a simple closed curve;
(iii) Each vertex has at least three edges incident with it and each face has at least three edges on its boundary;
(iv) Each face has exactly k edges, and therefore exactly k vertices.