How can I draw this double diagram in Latex?

Question

How can I draw this diagram in Latex?

Answer 1

Use the tikz-cd package:

\documentclass{article}
\usepackage{tikz-cd}
\begin{document}
\begin{tikzcd}
  G & B \arrow[l,"\psi"above]\arrow[d]\arrow[r,"g"] & C \
  & B/f(A) \arrow[lu,"\psi'"] \arrow[ru,"g'"below,"\simeq"above] &
\end{tikzcd}
\end{document}