showing identity element in a vector space [duplicate]

Question

I want to show identity element of a normed vector space with 1 that have extra line .How can I do it?

Answer 1

If by "1 that have extra line" you mean a double-struck 1, the following solution may be of interest to you.

\documentclass{article} % or some other suitable document class
\usepackage{dsfont}
\begin{document}
$\mathds{1}$
\end{document}