Non-real zeros of derivatives in the unit disc

Abstract

The main result establishes an estimate for the growth of a real meromorphic function $f$ on the unit disc $\Delta$ such that: (i) at least one of $f$ and $1/f$ has finitely many poles and non-real zeros in $\Delta$; (ii)~$f^{(k)}$ has finitely many non-real zeros in $\Delta$, for some $k\ge 2$.