# Overset alignment above text and inserted whitespace

I'd like to insert an annotation above equations without breaking the spacing of that equation. The annotation should be aligned to the left, and begin with an arrow that points down on the first symbol.

## Code

\newcommand{\hookdownleft}{\rotatebox[origin=b]{90}{$\Lsh$}}
\begin{dfn}
$\overset{\hookdownleft \text{family of sets from } \Omega \: \rightarrow \: \text{one set from } \Omega}{op} \in \mathcal{O} = \set{\text{set operations}}}$
\end{dfn}


## Desired

• Welcome t tex.sx. You might try using \mathrlap (provided by the mathtools package) to make LaTeX think the notation has no width. Feb 28 '19 at 18:17
• \mathrlap{overset{...}{..}} doesn't do any good. The annotation and the rest of the definition get moved to the beginning of the line, but the symbol above the annotation (op) stays in place, creating overlapping text.
– mxs
Feb 28 '19 at 18:32
• The \mathrlap should go inside the \overset: \overset{\mathrlap{\hookdownleft \text{family of sets ...}}}. Feb 28 '19 at 19:10
• Feb 28 '19 at 19:13

As pointed by Barbara Beeton, the simplest solution uses \mathrlapfrom mathtools inside the first argument of \overset. I added a \mathstrut to the second argument, to ensure a correct vertical spacing between the overset thing and the main line of equation:

\documentclass{article}

\usepackage{mathtools, amsthm, amssymb}
\DeclarePairedDelimiter{\set}\{\}
\usepackage{rotating, bigstrut}
\newcommand{\hookdownleft}{\rotatebox[origin=b]{90}{$\Lsh$}}
\theoremstyle{definition}
\newtheorem{dfn}{Definition}

\begin{document}

\begin{dfn}
$\overset{\mathrlap{\hookdownleft \text{family of sets from } \Omega \: \rightarrow \: \text{one set from } \Omega}}{op\mathstrut} \in \mathcal{O} = \set{\text{set operations}}$
\end{dfn}

\end{document}


• I'd upvote your answer, but I don't have enough reputation. I'm guessing I should have provided a more complete code example.
– mxs
Mar 1 '19 at 17:38