[Tex/LaTex] MacTeX 2019 gives “! LaTeX3 Error: Control sequence \not= already defined.”

Question

I have a document, that compiles fine on MacTeX 2017, which is installed on my desktop machine. I now installed MacTeX 2019 on my laptop and get this cryptic error:

(/usr/local/texlive/2019/texmf-dist/tex/latex/unicode-math/unicode-math-table.t
ex)

! LaTeX3 Error: Control sequence \not= already defined.

For immediate help type H <return>.
 ...                                              

l.3954 \NewNegationCommand { = }    { \neq   }

? 

Does anyone understand what this is about?

---

Edit:

MWE:

\documentclass[usenames,dipsnames,article,oneside]{memoir}
\usepackage{fontspec}
\usepackage[lining]{ebgaramond}
\usepackage[cmintegrals,cmbraces]{newtxmath}
\usepackage{ebgaramond-maths}
\usepackage{amssymb}
\usepackage{unicode-math}

\begin{document}
Test
\end{document}

Gives:

$ latexmk -pdf -lualatex test.tex
[...]
(/usr/local/texlive/2019/texmf-dist/tex/latex/unicode-math/unicode-math-table.t
ex)

! LaTeX3 Error: Control sequence \not= already defined.

For immediate help type H <return>.
 ...                                              

l.3954 \NewNegationCommand { = }    { \neq   }

? 

Answer 1

The example fails also on my TeX Live (MacTeX) 2017, probably because of updates you didn't apply.

The problem is simple: you are using too many math font packages. Loading newtxmath before ebgaramond-maths is recommended, because the latter only acts on the operators and letters math groups, not on symbols and largesymbols.

If you load unicode-math, all these settings to math fonts will be completely discarded and you'd get Latin Modern Math.

If you add

\[
abc+\int f(x)\,dx
\]

to your test document and compile skipping past the errors, you get

Removing \usepackage{unicode-math} not only removes the errors, but produces