How to write this symbol for a Banach algebra?

Question

How to write the following symbol in LaTeX

that's used for Banach algebras.

Answer 1

It is a fraktur "E".

\documentclass{article}
\usepackage{amssymb}
\begin{document}
$\mathfrak{E}_p(I)$
\end{document}

Interestingly, while http://detexify.kirelabs.org/classify.html is usually very good with this, I was not able to get auto-recognition of the fraktur E.