On global offensive k-alliances in graphs
  We investigate the relationship between global offensive $k$-alliances and some characteristic sets of a graph including $r$-dependent sets and $\tau$-dominating sets. As a consequence of the study, we obtain bounds on the global offensive $k$-alliance number in terms of several parameters of the graph. 
Sergio Bermudo, Juan A. Rodriguez-Velazquez, Jose M. Sigarreta, Ismael   G. Yero