GraphSum[g_1, g_2, ...] constructs the graph resulting from joining the edge lists of graphs g_1, g_2, and so forth.

GrayCodeKSubsets[l, k] generates k-subsets of l in Gray code order.

GrayCodeSubsets[l] constructs a binary reflected Gray code on set l.

GrayGraph returns a 3-regular, 54-vertex graph that is edge-transitive but not vertex-transitive\[LongDash]the smallest known such example.

HamiltonianPath[g] finds a Hamiltonian path in graph g if one exists. HamiltonianPath[g, All] gives all Hamiltonian paths of graph g.

HasseDiagram[g] constructs a Hasse diagram of the relation defined by directed acyclic graph g.

Heapify[p] builds a heap from permutation p.

HeapSort[l] performs a heap sort on the items of list l.

HeawoodGraph returns a smallest (6, 3)-cage, a 3-regular graph with girth 6.

HerschelGraph returns a graph object that represents a Herschel graph.