The forcing convexity number of a graph

For two vertices u and v of a connected graph G, the set I(u,v) consists of all those vertices lying on a u-v geodesic in G. For a set S of vertices of G, the union of all sets I(u, v) for u, v is an element of S is denoted by I(S). A set S is a convex set if I(S) = S. The convexity number con(G) of G is the maximum cardinality of a proper convex set of G. A convex set S in G with \S\ = con(G) is called a maximum convex set. A subset T of a maximum convex set S of a connected graph G is called a forcing subset for S if S is the unique maximum convex set containing T. The forcing convexity number f (S, con) of S is the minimum cardinality among the forcing subsets for S, and the forcing convexity number f (G, con) of G is the minimum forcing convexity number among all maximum convex sets of G. The forcing convexity numbers of several classes of graphs are presented, including complete bipartite graphs, trees, and cycles. For every graph G, f (G, con) less than or equal to con(G). It is shown that every pair a, b of integers with 0 less than or equal to a less than or equal to b and b greater than or equal to 3 is realizable as the forcing convexity number and convexity number, respectively, of some connected graph. The forcing convexity number of the Cartesian product of H x K-2 for a nontrivial connected graph H is studied.