Answer by Zarko for Please help to modify the \draw[ ->] in tikzpicture to have the overset effect \overset{..}{\to}?

With tikz-cd package?

\documentclass[margin=3mm]{standalone}\usepackage{tikz-cd}\begin{document}    \begin{tikzcd}[sep=scriptsize] A\rar["ab"] & B\rar["bc"] & C  \\ D           & E            & F  \end{tikzcd}\end{document}

Image may be NSFW.
Clik here to view.

For other possibilities of drawing commutative diagrams see package documentation.