In this paper we provide a catalog of the minimal blocks with 10 and fewer vertices, togel her with a discussion of the methods and theorems used to produce the catalog. In addition, we prove a theore m which is a strengthening of a similar theorem of Fleischner [2] on the structure of minimal blocks.Key words: Blocks; combinatorics; examples of graphs; graph theory; minimal blocks; planar graphs; thickness of graphs; two-connected graphs.
Description of the CatalogThe majority of the definitions used here will be found in (3),1 with the terms "point", "line", and "cycle" replaced by vertex, edge, and circuit. In particular, a block is a connected graph with no cut vertex, and a block is minimal if no spanning subgraph of the block with fewe r edges is also a block. We consider the graph with one vertex and no edges (the vertex graph) and the graph with two vertices and a single edge joining them (the link graph) to be minimal blocks. To distinguish between a path p and the graph which contains exactly the edges and vertices of p, we denote the graph by Ipl; for simplicity of terminology, we will refer to both p and Ipl as "paths." If p is a path, Let A!, . .. , Ak be k disjoint graphs which are paths, with k ;;,; 2, such that path A i contains mi vertices, for each i E {I, ... , k}, with m, ;;,; m2 ;;,; ... ;;,; mk ;;,; 1. Let a and,B b e vertices not in., k}, let ai be a Hamiltonian path inAi. Let the graph P (ml, m2, where X(G) denotes the edge set of graph G) such that A" . . . , Ak are sub graphs of P. We call P(ml, . . . , mk) a partition graph; clearly a partition graph with n vertices is completely determined up to isomorphism by a partition of the integer n -2. Further, it is clear that each partition graph is a minimal block. In the sequence m" . . . , mk, if m s+, = m s+2 = . . . = m s+,. for some integer s and integer r;;'; 2, we may write m" . . . , mk in the form m" . .. m s , r X ms+l, ms+r+I, . . . , mk. For example, P(3, 4 X 2) is shown in figure 1. Using this notation, the catalog at the end of this paper gives all minimal blocks with 10 and fewer vertices_ Above each of the drawings of a graph with 7 or more vertices is a sequence in parentheses_ This sequence is the degree sequence of the associated graph, i_e_, the sequence of degrees of the vertices of the graph in descending order. The