How does one TeX a blank?

Question

By blank, I'm looking to TeX something like this:

$\{\emptyset\}$ _ $\{\emptyset,\{\emptyset\}\}$, but I want the _ to look more like a longer blank as you'd see in a fill-in-the-blank type of question. Thanks.

Answer 1

You can use \underline with an argument of \hspace. For example,

\documentclass{article}
\begin{document}
$\emptyset$\underline{\hspace{1in}}$\emptyset,\emptyset$
\end{document}

Answer 2

\documentclass[11pt]{article}

\begin{document}
foo\textvisiblespace bar
foo\_bar 
foo\rule{1em}{0.5pt}bar
foo\rule[-2pt]{1em}{0.5pt}bar
foo~\rule[0.5ex]{1em}{0.5pt}~bar

\end{document}