Seeking two headed harpoon symbol

Question

There are several answers here about combining symbols, but I still decided to post this one since it is so simple, also maybe there is a ready symbol in some package that someone knows.

I am using

\def\paronto{{\rightharpoonup\kern-1.5ex\rightharpoonup\kern.5ex}}

which produces things like

and I have no idea whether it is robust enough - my kernings were adjusted by hand.

Who knows a better way?

Answer 1

You can typeset a harpoon, back space and typeset another one:

\documentclass{article}
\usepackage{amsmath}

\newcommand{\paronto}{%
  \rightharpoonup\mathrel{\mspace{-15mu}}\rightharpoonup
}

\begin{document}

$f\colon X\paronto Q$

\end{document}

With the help of trimclip you can make the symbol to have the same dimension as the single headed arrow:

\documentclass{article}
\usepackage{amsmath}
\usepackage{trimclip}

\DeclareRobustCommand{\paronto}{%
  \clippedrightharpoonup\mathrel{\mspace{-15mu}}\rightharpoonup
}
\makeatletter
\newcommand{\clippedrightharpoonup}{%
  \mathrel{\mathpalette\clipped@rightharpoonup\relax}%
}
\newcommand{\clipped@rightharpoonup}[2]{%
  \sbox\z@{$\m@th#1\mspace{3mu}$}%
  \smash{\clipbox{{\wd\z@} 0pt 0pt {-\width}}{$\m@th#1\rightharpoonup$}}%
}
\makeatother

\begin{document}

$f\colon X\paronto Q_{\paronto}$

$f\colon X\rightharpoonup Q_{\rightharpoonup}$

\end{document}

With a rounded stem:

\documentclass{article}
\usepackage{amsmath}
\usepackage{trimclip}

\DeclareRobustCommand{\paronto}{%
  \clippedrightharpoonup\mathrel{\mspace{-15mu}}\rightharpoonup
}
\makeatletter
\newcommand{\clippedrightharpoonup}{%
  \mathrel{\mathpalette\clipped@rightharpoonup\relax}%
}
\newcommand{\clipped@rightharpoonup}[2]{%
  \sbox\z@{$\m@th#1\mspace{6mu}$}%
  \clipbox{0pt 0pt {\dimexpr\width-.5\wd\z@} 0pt}{$\m@th#1\rightharpoonup$}%
  \smash{\clipbox{{\wd\z@} 0pt 0pt {-\width}}{$\m@th#1\rightharpoonup$}}%
}
\makeatother

\begin{document}

$f\colon X\paronto Q_{\paronto}$

$f\colon X\rightharpoonup Q_{\rightharpoonup}$

\end{document}