configuration sets; a right place for ping-pong arguments

Giving a condition for the amenability of groups, rosenblatt and willis first introducedthe concept of configuration. in this paper, we investigate the relationship between ping-pong lemma and configuration sets, and show that only one configuration set is enough to ensure that several elements in a group generates a free subgroup of that group. using only one two-sided configuration sets, we give, in a sense, a generalization of this result to polycyclic or fc-groups. finiteness and paradoxical decompositions of groups, are other properties which can be characterized with only one configuration set.