Integral sign using eulervm and newpx

Question

I've tried to load eulervm alongside newpxtext and newpxmath, and this has worked fine until I attempted to construct an integral using \int. The integral sign simply doesn't appear:

    \documentclass{article}

    \usepackage{newpxtext,newpxmath} 
    \usepackage{eulervm}

    \begin{document} 
    \[\int_a^b f(x)\, dx\] 
    \end{document}

Have I missed something?

Answer 1

One can redeclare the integral operator, \intop:

\documentclass{article}
\usepackage{newpxtext,newpxmath} 
\usepackage{eulervm}
\DeclareMathSymbol\intop \mathop {largesymbols}{"52}
\begin{document} 
\[\int_a^b f(x)\, dx  \quad\textstyle\int_a^b f(x)\, dx\] 
\end{document}

Alternately, one could save a version of \intop before loading newpxmath and then restore it afterwards:

\documentclass{article}
\let\svintop\intop
\usepackage{newpxtext,newpxmath} 
\let\intop\svintop
\usepackage{eulervm}
\begin{document} 
\[\int_a^b f(x)\, dx  \quad\textstyle\int_a^b f(x)\, dx\] 
\end{document}

As a third way, one could just load the euler package, instead of eulervm.

\documentclass{article}
\usepackage{newpxtext,newpxmath} 
\usepackage{euler}
\begin{document} 
\[\int_a^b f(x)\, dx  \quad\textstyle\int_a^b f(x)\, dx\] 
\end{document}

---

DISCUSSION

All this happens for two reasons: because eulervm does not explicitly declare \intop and also because newpxmath redefines \intop (by default) with

\let\intop=\intslop

where

\re@DeclareMathSymbol{\intslop}                {\mathop}{largesymbols}{"AF}

This "AF is a different glyph slot than the "52 used by eulervm. And \intop is an integral part of \int, as defined in newpxmath as

\def\int{\DOTSI\intop\ilimits@}

This MWE shows the discussion explicitly:

\documentclass{article}
\sbox0{DEFAULT: \meaning\intop}
\usepackage{newpxtext,newpxmath} 
\sbox2{NEWPXMATH: \meaning\intop}
\usepackage{eulervm}
\sbox4{EULER DOES NOT FIX: \meaning\intop}
\DeclareMathSymbol\intop \mathop {largesymbols}{"52}
\sbox6{REDECLARED: \meaning\intop}
\begin{document} 
\[\int_a^b f(x)\, dx  \quad\textstyle\int_a^b f(x)\, dx\] 

\box0

\box2

\box4

\box6
\end{document}

---

POSTSCRIPT

The package euler does not suffer the same problem because it explicitly declares the \intop symbol to slot "52.