in books and papers often a theorem contains several parts, labeled (i), (ii), ...

\begin{theorem} Let $A$ be a finite set and $f$ a map from $A$ to itself. The following statements are equivalent: \begin{itemize} \item[(i)] $f$ is injective. \item[(ii)] $f$ is surjective. \item[(iii)] $f$ is a bijection. \end{itemize} \end{theorem}

I want refer to part(i) of this theorem but I do not know how to do it. How can I do that? I'd be very grateful for any help.