[Tex/LaTex] Compiling Error – amsmath, MultiIntegral — Command \iint already defined

Question

I get the following error:

I tried to do the solution in this answer, but get the same error. Error in compilation

What to do?

Here is my preamble:

\documentclass[phd,tocprelim]{userdefined}
\usepackage{graphicx,pstricks}
\usepackage{graphics}
\usepackage{moreverb}
\usepackage{subfigure}
\usepackage{epsfig}
\usepackage{subfigure}
\usepackage{txfonts}
\usepackage{palatino}
\usepackage{pdfpages}
\usepackage{rotating}
\usepackage{caption}
 \captionsetup[subfigure]{position=bottom}
 \usepackage{color}
\usepackage{hyperref}
\usepackage{lscape}
\usepackage{rotating}
\usepackage{longtable}
\usepackage{booktabs}
\usepackage{fixltx2e}
\usepackage[flushleft]{threeparttable}
\usepackage{geometry}
\usepackage{natbib}
\usepackage{float}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsthm}
\usepackage{wasysym}

Answer 1

The txfonts package already defines the \iint macro (and a few others), so that when amsmath tries to load them, it cannot.

Solution: load txfonts after amsmath, amssymb and amsthm.

But txfonts is deprecated. You should use newtxtext and newtxmath instead.

You also don't need graphics when you have graphicx. Actually, you shouldn't ever use graphics, it's deprecated. Same for color: use xcolor.

The subfigure package (which you were loading twice) is also deprecated, you should use subcaption instead (but I'll leave this one or your document will break everywhere. But consider updating).

Also, hyperref should be the last package loaded, with very few exceptions.

Finally, fixltx2e doesn't do anything these days. Just remove it.

From Bernard's comment: epsfig shouldn't be used any more (cf. l2tabu): graphicx does the same job.

(There are probably a few more I forgot to mention. If someone knows, feel free to edit/comment.)

It looks like you are using a very, very old template. You should probably update it.

Anyway, your preamble should look like this by now:

\documentclass[phd,tocprelim]{cornell}
\usepackage{graphicx,pstricks}
\usepackage{moreverb}
\usepackage{subfigure}% Leaving this one, but you should change to subcaption
\usepackage{palatino}
\usepackage{pdfpages}
\usepackage{rotating}
\usepackage{caption}
 \captionsetup[subfigure]{position=bottom}
 \usepackage{xcolor}
\usepackage{lscape}
\usepackage{rotating}
\usepackage{longtable}
\usepackage{booktabs}
\usepackage[flushleft]{threeparttable}
\usepackage{geometry}
\usepackage{natbib}
\usepackage{float}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsthm}
\usepackage{txfonts}
\usepackage{wasysym}
\usepackage{hyperref}