Minimal commutative diagram drawn with the tikz-cd library — square shape with four objects A, B, C, D and four labelled morphisms f, g, h, k. The library handles arrow routing, label placement, and spacing automatically. Drop-in replacement for old XY-pic diagrams.
\documentclass[border=10pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{cd}
\begin{document}
\begin{tikzcd}[row sep=large, column sep=large]
A \arrow[r, "f"] \arrow[d, "g"'] & B \arrow[d, "h"] \\
C \arrow[r, "k"'] & D
\end{tikzcd}
\end{document}
