On a boundary property of Blaschke products (Q6111819)

Let \(\Delta\) denote the unit disc in \(\mathbb{C}\) with boundary \(T\). In the paper the authors prove the following theorem concerning the boundary behavior of Blaschke products. Let \(E\) be a subset of \(T\). Then there exists a Blaschke product on \(\Delta\) which has no radial limits on \(E\) but has unrestricted limits at each point of \(T\setminus E\) if and only if \(E\) is a closed set of measure zero.