More results on greedy defining sets

The greedy defining sets of graphs were appeared first time in [M. Zaker, Greedy defining sets of graphs, Australas. J. Combin, 2001]. We show that to determine the greedy defining number of bipartite graphs is an NP-complete problem. This result answers affirmatively the problem mentioned in the previous paper. It is also shown that this number for forests can be determined in polynomial time. Then we present a method for obtaining greedy defining sets in Latin squares and using this method, show that any $n\times n$ Latin square has a GDS of size at most $n^2-(n\log n)/4$. Finally we present an application of greedy defining sets in designing practical secret sharing schemes.