Arrow structure with under arrows

Question

So I was transcribing a lecture for a college asignment and when I got to this formula I just don't know how to code it. Do someone know how to code it in Latex? Thanks in advance.

This is the figure I want to code

Answer 1

Such diagrams can be produced with tikz-cd, or, practically equivalently the cd library of tikz. You probably want the bounding box to be accurate, too, to which end you may use the bbox library.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{bbox,cd}
\begin{document}
\begin{tikzcd}[bezier bounding box]
 A \arrow[r,"f"]& B \arrow[l,"g",out=-15,in=-45]\\
\end{tikzcd}
\end{document}