Motivated by work of Yu.L. Shmul'yan a pre-order and an equivalence relation on the set of operator-valued Schur class functions are introduced and the behavior of Redheffer linear fractional ...

Let ≤c be computable the reducibility on computably enumerable equivalence relations (or ceers). We show that for every ceer R with infinitely many equivalence classes, the index sets {i : Ri ≤c R} ...