ABSTRACT

Let us denote by Rec(E, X) the set of all recognizable E — X-languages. We will study some algebraic properties of this set, beginning with some operations under which it is closed.

Now we consider mappings which transform trees from one language into trees from another one. Let E := ff, i E I} be a set of operation symbols of type Ti = (n2)ter, where L is n2-ary, n2 E N and let Q = {g3 j E J} be a set of operation symbols of type T2 = (n3)3E j where g3 is n3-ary. We denote by WE(X) and by W0(Y) the sets of all terms of type ri and T2, respectively, where X and Y are alphabets of variables.