[Tex/LaTex] Symbol of compactly embedding

Question

What latex command does this symbol allow?

Answer 1

With stackengine:

\documentclass[]{article}
\usepackage{stackengine}
\newcommand\dhookrightarrow{\mathrel{%
  \ensurestackMath{\stackanchor[.1ex]{\hookrightarrow}{\hookrightarrow}}
}}
\begin{document}
$a \dhookrightarrow b$
\end{document}

If you need it across math styles:

\documentclass[]{article}
\usepackage{stackengine,scalerel}
\newcommand\dhookrightarrow{\mathrel{\ThisStyle{\abovebaseline[-.6\LMex]{%
  \ensurestackMath{\stackanchor[.15\LMex]{\SavedStyle\hookrightarrow}{%
  \SavedStyle\hookrightarrow}}}}}}
\begin{document}
$a \dhookrightarrow b$\par
$\scriptstyle a \dhookrightarrow b$\par
$\scriptscriptstyle a \dhookrightarrow b$\par
\end{document}