How to express “null T” in math mode [duplicate]

Question

What is the correct way to express "null T", which represents the nullspace of a linear map T?

I've been doing \newcommand{\nullspace}{\text{null }} which is a hack, but I want there to be a space between "null" and "T".

One problem with my approach is that the "null" is italic when it's written within a theorem etc, but in a standard express it's not italic. I would prefer it to always be non-italic.

Answer 1

\documentclass{article}
\usepackage{amsmath,thmtools}
\DeclareMathOperator{\nullspace}{null}
\declaretheorem{theorem}
\begin{document}
\(\nullspace T\)
\begin{theorem}{xyz}
blah $\nullspace T$
\end{theorem}
\end{document}