I have used the template presented in this answer to create the following document.
\documentclass{amsart}
\usepackage{enumitem}
\usepackage[nameinlink]{cleveref}
\newtheorem{proposition}{Proposition}[section]
\crefname{proposition}{Prop.}{props.}
\newlist{enumprp}{enumerate}{1}
\setlist[enumprp]{label=\upshape(\alph*),ref=\upshape\theproposition(\alph*)}
\crefalias{enumprpi}{proposition}
\makeatletter
\newcounter{subcreftmpcnt}
\newcommand\alphsubformat[1]{(\alph{#1})}
\newcommand\subcref[2][\alphsubformat]{
\ifcsname r@#2@cref\endcsname
\cref@getcounter {#2}{\mylabel}
\setcounter{subcreftmpcnt}{\mylabel}
\alphsubformat{subcreftmpcnt}
\else ?? \fi}
\makeatother
\begin{document}
\begin{proposition}
\begin{enumprp}
\item One
\item Two
\end{enumprp}
\end{proposition}
\begin{proof}
\begin{enumerate}
\item One
\item Two
\end{enumerate}
\end{proof}
\end{document}
The result is
Observe that the numbering of the items in the proposition statement is (a), (b), whereas the numbering of the items in the proof is (1), (2).
How can I make the numbering in the statement (1), (2)? (Actually, I'd rather the numbering be 1., 2.)

enumitemenvironment, so I use theenumerateenvironment, however other times theenumitemenvironment is indispensable to me, since I need to label the items. In either case, I always use theenumerateenvironment in the proof. – Evan Aad Sep 07 '18 at 11:01