Issues using newtheorem

Question

I'm trying to use \newtheorem.

Here's my small sty file mystyle.sty

\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsthm}
\newtheorem{action}{$\checkmark$ Action}
\newtheorem{law}{$\bigodot$ Law}
\newtheorem{fact}{$\boxdot$ Fact}
\newtheorem{warn}{$\warning$ Caveat}

Here's the tex file:

\documentclass[11pt]{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{amssymb}
%\usepackage{arevmath}
\usepackage{mystyle}
\begin{document}
\section{Head}
\begin{law}
The world is round
\end{law}
\begin{fact}
\(g =99.8 m/s^2\)
\end{fact}
\begin{action}
Teach co-recursion before recursion
\end{action}
\begin{warn}
 Beware
\end{warn}
\end{document}

This is with package arevmath

This is without arevmath

So now the questions:

1. I want the warning symbol which is in arevmath but the general look of without arevmath is better. How to manage both?
2. The content is coming in italic. But the examples I find for using newtheorem it comes normal roman. Is something else wrong?? eg...
3. I picked up the eg from an inline source that uses \makeatletter. I'm not at all sure how to use it except for some vague directive: use in .tex not in .sty.

Answer 1

You want to use just the symbols provided by arevmath, not to change all math symbols to use it.

Actually, arevmath uses ams-mdbch and we see, in ams-mdbch.sty,

\xdef\checkmark{\noexpand\mathhexbox{\hexnumber@\symmathdesignA}D8}
\DeclareMathSymbol{\boxdot}{\mathbin}{mathdesignA}{"80}

The definition of \bigodot is the standard one, albeit using a different font. The command \warning is found in arevsymbols.tex and we see

\DeclareMathSymbol{\warning}{\mathalpha}{extraup}{125} % uni26A0

OK, the file ams-mdbch.sty has

\DeclareSymbolFont{mathdesignA}{MDA}{mdbch}{b}{n}
\SetSymbolFont{largesymbols} {normal}{OMX}{mdbch}{m}{n}

and in arevmath.sty we see

\DeclareSymbolFont{extraup}{U}{zavm}{m}{n}

Quite a chase! But we have all the ingredients. The only problem is \bigodot, but it can be solved.

\documentclass[11pt]{article}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{amssymb}
%\usepackage{arevmath}
\DeclareFontEncoding{MDA}{}{}
\DeclareFontSubstitution{MDA}{cmr}{m}{n}
\newcommand{\arevcheckmark}{{\usefont{MDA}{mdbch}{b}{n}\symbol{"D8}}}
\newcommand{\arevbigodot}{%
  $\vcenter{\hbox{\usefont{OMX}{mdbch}{m}{n}\symbol{"4A}}}$%
}
\newcommand{\arevboxdot}{{\usefont{MDA}{mdbch}{b}{n}\symbol{"80}}}
\newcommand{\arevwarning}{{\usefont{U}{zavm}{m}{n}\symbol{125}}}
\newtheorem{action}{\arevcheckmark\ Action}
\newtheorem{law}{\arevbigodot\ Law}
\newtheorem{fact}{\arevboxdot\ Fact}
\newtheorem{warn}{\arevwarning\ Caveat}
\begin{document}
\section{Head}
\begin{law}
The world is round
\end{law}
\begin{fact}
(g =99.8 m/s^2)
\end{fact}
\begin{action}
Teach co-recursion before recursion
\end{action}
\begin{warn}
Beware
\end{warn}
\end{document}

I left the wrong typesetting of the units in 9.8 m/s², fix it.

Answer 2

My current version thanks to egreg's help.
[Yeah the units are not proper. But that was a red herring for me anyway to produce some mwe; not something I currently need in my actual example]

\documentclass[11pt]{article}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsthm}
%\usepackage{arevmath}
\DeclareFontEncoding{MDA}{}{}
\DeclareFontSubstitution{MDA}{cmr}{m}{n}
\newcommand{\arevcheckmark}{{\usefont{MDA}{mdbch}{b}{n}\symbol{"D8}}}
%% \newcommand{\arevbigodot}{%
%%   $\vcenter{\hbox{\usefont{OMX}{mdbch}{m}{n}\symbol{"4A}}}$%
%% }
\newcommand{\arevboxdot}{{\usefont{MDA}{mdbch}{b}{n}\symbol{"80}}}
\newcommand{\arevwarning}{{\usefont{U}{zavm}{m}{n}\symbol{125}}}
\theoremstyle{definition}
\newtheorem{action}{\arevcheckmark\ Action}
\newtheorem{law}{(\odot)\ Law}
\newtheorem{fact}{(\boxdot)\ Fact}
\newtheorem{warn}{\arevwarning\ Caveat}
\begin{document}
\section{Head}
\begin{law}
The world is round
\end{law}
\begin{fact}
(g =99.8 m/s^2)
\end{fact}
\begin{action}
Teach co-recursion before recursion
\end{action}
\begin{warn}
Beware
\end{warn}
\end{document}