Hypermap operations of finite order

Duality and chirality are examples of operations of order 2 on hypermaps. James showed that the groups of all operations on hypermaps and on oriented hypermaps can be identified with the outer automorphism groups Out ∼= PGL2(Z) and Out + ∼= GL2(Z) of the groups = C2 ∗C2 ∗C2 and + = F2. We will consider the elements of finite order in these two groups, and the operations they induce

Unified bijections for planar hypermaps with general cycle-length constraints

We present a general bijective approach to planar hypermaps with two main results. First we obtain unified bijections for all classes of maps or hypermaps defined by face-degree constraints and girth constraints. To any such class we associate bijectively a class of plane trees characterized by local constraints. This unifies and greatly generalizes several bijections for maps and hypermaps. Second, we present yet another level of generalization of the bijective approach by considering classes of maps with non-uniform girth constraints. More precisely, we consider "well-charged maps", which are maps with an assignment of "charges" (real numbers) on vertices and faces, with the constraints that the length of any cycle of the map is at least equal to the sum of the charges of the vertices and faces enclosed by the cycle. We obtain a bijection between charged hypermaps and a class of plane trees characterized by local constraints

Maps on surfaces and Galois groups

A brief survey of some of the connections between maps on surfaces, permutations, Riemann surfaces, algebraic curves and Galois groups is given

Hypercubes as dessins d'enfant

We describe the action of the group GL2(Z) on embeddings of hypercubes on compact orientable surfaces, specifically classifying the elements of finite order that can change the genus of the underlying surface by an arbitrarily large amount. In doing so we give an explicit illustration of the kind of computations encountered in the study of dessins d'enfants in the hope that those new to the area may find such an explicit example useful