There are not two distinct Unicode points for the empty set and its variant symbol (they are just different forms of the same symbol). Find a font that has the circle form and use it.
\documentclass[12pt]{article}
\usepackage[fleqn]{amsmath}
\usepackage{unicode-math}
\usepackage[english,greek]{...
@Adam The first and third \setmathfont shouldn't be necessary in an ideal world (Latin Modern Math is the default of unicode-math), but they're unfortunately needed if different fonts are used for some ranges. With only the second declaration, two bugs of unicode-math show, which are corrected with the other two declarations. The order matters.
@egreg I used these lines of code and I get errors: Undefined control sequence. l.37 \setmathfont {Latin Modern Math} LaTeX Error: Missing \begin{document}. Undefined control sequence. l.38 \setmathfont[range=\varnothing ]{Asana Math} Missing $ inserted. <inserted text>
l.39 \setmathfont {Latin Modern Math} The control sequence at the end of the top line of your error message was never \def'ed. If you have misspelled it (e.g., `\hobx'), type `I' and the correct spelling (e.g., `I\hbox'). Otherwise just continue, and I'll forget about whatever was undefined.
Undefined control sequence.
l.39 \setmathfont {Latin Modern Math} The control sequence at the end of the top line of your error message was never \def'ed. If you have misspelled it (e.g., `\hobx'), type `I' and the correct spelling (e.g., `I\hbox'). Otherwise just continue, and I'll forget about whatever was undefined.
Why do you want to do your way? First amsmath, then unicode-math, then babel, then all font declarations. You may have to load the fonts by filename, so it should be latinmodern-math.otf and Asana-Math.otf
By the way, what's the meaning of declaring Artemisia as the sans serif font?
Sorry I had copied the previous file I change it when you told me. Still has a lot of errors. I didn't. I had troubles with languages so this is an answer form the site.
! ! fontspec error: "font-not-found" ! ! The font "Latin Modern Math" cannot be found. ! ! See the fontspec documentation for further information. ! ! For immediate help type H <return>. !............................................... l.48 \setmathfont{Latin Modern Math} |''''''''''''''''''''''''''''''''''''''''''''''' | A font might not be found for many reasons. | Check the spelling, where the font is installed etc. etc. | | When in doubt, ask someone for help! |...............................................
Cannot use \XeTeXOTcountfeatures with nullfont; not an OpenType Layout font.
<argument> \XeTeXOTcountfeatures \l_fontspec_font \l_fontspec_script_int \l_... l.48 \setmathfont{Latin Modern Math}
Notes/Propability and Statistics/Preamble.tex, line 48
Cannot use \XeTeXOTfeaturetag with nullfont; not an OpenType Layout font.
<argument> ...\XeTeXOTfeaturetag \l_fontspec_font \l_fontspec_script_int \l_... l.48 \setmathfont{Latin Modern Math}
Notes/Propability and Statistics/Preamble.tex, line 48
Missing = inserted for \ifnum.
Discussion between egreg and Adam
Discussion between egreg and Adam