Normality Criteria for Differential Monomials and the Sharpness of Lappan-type Theorems

Molla Basir Ahamed, Sanju Mandal, Nguyen Van Thin

A fundamental result of Lappan [Comment. Math. Helv. \textbf{49} (1974), 492-495.] states that a meromorphic function $f$ in the unit disk $\mathbb{D}$ is normal if and only if its…