I'm trying to put `\mathbb{R}` in an `\underset` of `\sup` in the following way:

```
\underset{x \in \mathbb{R}}{\sup}

```

However this sequence does not render as usual. I use following libraries:

```
\usepackage{amssymb,amsmath, amsthm}
\usepackage{enumitem}
\usepackage{microtype}
\usepackage{idxlayout}
\usepackage{amssymb}
\usepackage{lmodern}
\usepackage{amsmath}
\usepackage{float}
\usepackage{amsthm}
\usepackage{flexisym}
\usepackage{graphicx}
\usepackage{mathtools}

```

I'm new to LaTeX and not sure how to approach this problem. Please help.

Full MWE to reproduce this:

```
\documentclass[oneside,12pt,a4paper]{memoir}
\renewcommand{\baselinestretch}{1.15}
\let\memoldbibsection\bibsection
\let\bibsection\relax
\usepackage[nobysame]{amsrefs}
\let\bibsection\memoldbibsection 
\usepackage[right=2.7cm,left=3.5cm, top=2.7cm, bottom=2.5cm,includehead]{geometry}
\usepackage{amssymb,amsmath, amsthm}
\usepackage{enumitem}
\usepackage{microtype}
\usepackage{idxlayout}
\usepackage{amssymb}
\usepackage{lmodern}
\usepackage{amsmath}
\usepackage{float}
\usepackage{amsthm}
\usepackage{flexisym}
\usepackage{graphicx}
\usepackage{mathtools}

\makeindex
\makeindex[sym]

\setcounter{secnumdepth}{2}

\makeatletter

\begin{document}
$\underset{x \in \mathbb{R}}{\sup}$
\end{document}

```