sentences:  Denote by formula_1 the set of all finite subsets of a set formula_2.Likewise, for a positive integer formula_3, denote by formula_4 the set of all formula_3-elements subsets of formula_2.For a mapping formula_7, we say that a subset formula_8 of formula_2 is "free" (with respect to formula_10), if for any formula_3-element subset formula_12 of formula_8 and any formula_14, formula_15.