Coefficients of bounded nonvanishing functions

The Krzyż conjecture revisited

“…Thus a z ℓ −j = 0. In either case we have a z ℓ −j b j = 0 and so (17) holds. We now get b z ℓ = 0 since a 0 > 0.…”

“…The authors of [13] gave their own proof of (4) and mentioned two other possible proofs. Kortram [17] later gave yet another proof. We also mention a result on the structure of extremal functions for more general coefficient problems that follows directly from an earlier work of Hummel [12], as was pointed out by Sakaguchi [30,Theorem C].…”