A constructive proof of the Chang-Marshall theorem

In the paper one gives constructive proofs (without the use of the space of maximal ideals of the algebra $H^{\infty}$) of the Marshall-Chang theorem and of a theorem of T. H. Wolff. These theorems are proved in the paper in a unique manner with the use of a lemma which connects the level lines of a positive harmonic function in a circle with the level lines of the inner function.