Big mess with my LaTeX code: I want the curvy integral back!

Question

The truth is that, up to now, I have used a template that I created long ago to write my lecture notes. All seems OK, but the only thing that's been bothering me lately is that the integral sign in my equations is not curved (as it should), but it appears rigid and vertical, just like the left integral in this picture:

I really don't know what package I'm missing (or what package I'm importing that does this). I've read several manuals, but can't find the solution to my problem :-(. The packages that I import before the \begin{document} are:

\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amsthm,mathabx,wrapfig} 
\usepackage[spanish]{babel} % I'm writing lecture notes in spanish!
\usepackage[utf8x]{inputenc} 
\usepackage[margin=1.25in]{geometry}
\usepackage{graphics,graphicx,ctable,booktabs}
\usepackage{ccaption}
\usepackage{fancyhdr}

How do I fix this problem?

Answer 1

The problem is in the mathabx package, which changes many symbols.

You have some possible strategies:

1. load only two of the three families provided by mathabx:

   \usepackage[matha,mathb]{mathabx}
   

2. revert the integral to the original after having loaded mathabx:

   \let\orintop\intop
   \usepackage{mathabx}
   \let\intop\orintop
   

   (some other adjustments may be necessary for multiple integrals)

3. don't load mathabx and follow some of the tricks present on this site for loading only the symbols from it that you really need, for example

   https://tex.stackexchange.com/a/14406/4427

   https://tex.stackexchange.com/a/19986/4427

   https://tex.stackexchange.com/a/39314/4427