I am writing my thesis and am using the amsmath package for the theorem/lemma/definition/proof environments. I am having trouble figuring out how to simultaneously have the "definition" environment in plain text and then I manually italicize the definition and having the proof environment work correct. I have been able to get both to work independently following the information on overleaf's site:
https://www.overleaf.com/learn/latex/Theorems_and_proofs
To get the proof environment to work, my preamble looks like the below code:
\usepackage{amsmath}
\newtheorem{thm}{Theorem}[section]
\newtheorem{prop}[thm]{Proposition}
\newtheorem{lemma}[thm]{Lemma}
\newtheorem{ex}[thm]{Example}
\theoremstyle{definition}
\newtheorem{dfn}[thm]{Definition}
As an example, consider this snippet of code:
\begin{dfn}
A \textit{group} is a set blah blah blah
\end{dfn}
\begin{proof}
does it work?
\end{proof}
This is what the output looks like using the above preamble:
As you can see, the defintion is fully italicized. This doesn't look the way I want it to until I add \usepackage{amsthm}, like below:
\usepackage{amsmath}
\usepackage{amsthm}
\newtheorem{thm}{Theorem}[section]
\newtheorem{prop}[thm]{Proposition}
\newtheorem{lemma}[thm]{Lemma}
\newtheorem{ex}[thm]{Example}
\theoremstyle{definition}
\newtheorem{dfn}[thm]{Definition}
This is what the same code looks after loading amsthm:
When I compile my document using the second example for the preamble, my definitions look how I want them to, but the proof environment no longer works correctly. The word "proof" is no longer in bold and the standard square QED icon does not show up. I get the error "Something's wrong--maybe missing a \item" all over my document.
Does anyone know how to resolve both of these issues simultaneously? This is not my entire preamble, I can add the rest if needed. Also, I am not typing my text directly in the file that is loading the document. I am using a separate file introduction.tex file and then using the command "\include{introduction}. I am not sure if this matters but I thought it was somewhat relevant.
edit: My documentlcass is unique to my university because all of the formatting and whatnot is regulated. A template can be found on overleaf:
https://www.overleaf.com/latex/templates/purdue-university-thesis-template/rkjkbcgbcdck
amsthm
?amsmath
andamsthm
are independent of each other. You don't have aproof
environment withoutamsthm
.\documentclass{...}
and end with\end{document}
.