sentences:  If is a quantifiers block then we will call formula_73 the iteration operator, which is defined as written formula_61 time.One should pay attention that here there are formula_75 quantifiers in the list, but only variables and each of those variable are used formula_61 times.We can now define formula_60 to be the FO-formulae with an iteration operator whose exponent is in the class formula_61, and we obtain those equalities