[Tex/LaTex] Proposition command doesn’t work

theoremsthesis

Please refer to the below code:

\documentclass[a4paper,11pt]{report} 
\usepackage{a4wide}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{graphicx}
\usepackage{url}
\usepackage{fixltx2e}
\usepackage{caption}
\usepackage{subcaption}
\oddsidemargin 0.0in
\textwidth 6.27in
\topmargin -0.5in
\textheight 9.69in
\footskip 0.5in
\urlstyle{sf}
\usepackage{fancyhdr}
\makeatletter
\newcommand*{\rom}[1]{\expandafter\@slowromancap\romannumeral #1@}
\makeatother
\usepackage{epstopdf}
\usepackage{multirow}
\usepackage{subfig}
\linespread{1.3}
\usepackage{float}
\usepackage{enumerate}
\usepackage{enumitem}
\usepackage{multirow}
\usepackage{amsmath, amsthm, amssymb}

\begin{document}
\begin{prop}
1. $x=Y+z$ \\
2. $\alpha=1-x$
\end{prop}
\end{document} 

Best Answer

You need to define the structure using \newtheorem (refer to the documentation of the amsthm package for further details on the optional arguments of this command):

\documentclass[a4paper,11pt]{report} 
\usepackage{amsmath, amsthm, amssymb}

\newtheorem{prop}{Proposition}

\begin{document}
\begin{prop}
\begin{enumerate}
\item $x=Y+z$
\item $\alpha=1-x$
\end{enumerate}
\end{prop}
\end{document}

enter image description here

Not related to the question, but I replaced you manual enumeration with an enumerate environment. You are loading some packages more than once; this should be avoided. Also changes to the page layout should be better done using the geometry package.

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