Turn off locally one package

Question

In the following code, I would like to show two different formatting styles: one using the package nath output, and another showing the default output.

How can I do that?

% Source : http://tex.stackexchange.com/questions/1023/vertically-asymmetric-size-variation-for-parentheses

\documentclass[10pt,a4paper]{article}
    \usepackage[utf8x]{inputenc}
    \usepackage{ucs}
    \usepackage{amsmath}
    \usepackage{amsfonts}
    \usepackage{amssymb}

    \usepackage{nath} % The usefull package.

    \newcommand{\formulaOne}{\sum_{0 \le i \le m \\ 0 < j < n} P(i,j)}
    \newcommand{\formulaTwo}{1 + \frac{1 + x^2}{1 - \frac{x}{2}}}


\begin{document}

\section{With nath}

\begin{equation}
    ( \formulaOne ) = [ \formulaTwo ]
\end{equation}


\section{Without nath}

\begin{equation}
    \left( \formulaOne \right) = \left[ \formulaTwo \right]
\end{equation}


\end{document}

Answer 1

this works:

\documentclass[10pt,a4paper]{article}
\usepackage{amsmath}
\begin{document}

\section{Without nath}   
\begin{equation}
    \left( \sum_{0 \le i \le m \\ 0 < j < n} P(i,j) \right) 
    = \left[ 1 + \frac{1 + x^2}{1 - \frac{x}{2}} \right]
\end{equation}

\section{With nath}

\makeatletter
\input{nath.sty}
\makeatother
\begin{equation}
    ( \sum_{0 \le i \le m \\ 0 < j < n} P(i,j) ) 
      = [ 1 + \frac{1 + x^2}{1 - \frac{x}{2}} ]
\end{equation}

\end{document}

Answer 2

The nath package changes too much of the default setting that such a project, even if it was feasible (I don't think so, though), would require a gigantic effort.

The best strategy is to prepare the samples with the standalone class and to import them as PDF graphics.