I cannot use amsmath package

Question

I try to compile my latex but it doesn't work. It shows the following error

Command \iint already defined. ...d{\iint}{\DOTSI\protect\MultiIntegral{2}}

The command that I'm using is as follows:

\documentclass{aip-cp}

\usepackage{amsmath}
\usepackage[numbers]{natbib}
\usepackage{rotating}
\usepackage{graphicx, amsfonts, amssymb, longtable}
\let\openbox\relax
\usepackage{amsthm, amsthm}

\begin{document}

\end{document}

Somebody please help me.

Answer 1

As mentioned by others this comes from the fact that the class loads txfonts which defines some symbols that amsmath also defines.

Here is an even shorter MWE:

\documentclass[a4paper]{article}
\usepackage{txfonts}
\usepackage{amsmath}
\begin{document}
test
\end{document}

You can use the normal \let...\relax trick to remove these symbols. Turns out there are four:

\documentclass[a4paper]{article}
\usepackage{txfonts}
\let\iint\relax
\let\iiint\relax
\let\iiiint\relax
\let\idotsint\relax
\usepackage{amsmath}
\begin{document}
test
\end{document}