Introduction. Our terminology is from [1]. We consider the collection of all r.e. (recursively enumerable) sets arranged in an effective sequence co1,co2,--•,«;,••• as in the Post-Kleene enumeration, i.e.,cü¡ is the set of all numbers satisfying the condition (3y)T1(i,x, y), where 7\(z,x,y) is the Kleene predicate (cf. [2]). A number set a. is called productive iff there exists a recursive func...