How to put a square inside a commutative diagram?
The right way with tikz-cd
is to use a "phantom" arrow as in
\arrow[dr, phantom, "\square"]
MWE (I've used some code to reproduce the picture and not yours):
\documentclass{article}
\usepackage{amssymb}
\usepackage{tikz-cd}
\begin{document}
\begin{tikzcd}
X'' \arrow[r, "g'"] \arrow[d] & X' \arrow[r, "g"] \arrow[d] \arrow[dr, phantom, "\square"] & X \arrow[d] \\
S'' \arrow[r, "f'"'] & S' \arrow[r, "f"'] & S
\end{tikzcd}
\end{document}
Two solutions: one with pstricks
and a psmatrix
environment, the other with tikz-cd
, in which I use the short syntax for arrows:
\documentclass{article}
\usepackage{mathtools, amssymb}
\usepackage{pst-node, auto-pst-pdf}
\usepackage{tikz-cd}
\begin{document}
\texttt{psmatrix solution: }
\[ \psset{arrows=->, arrowinset=0.15, linewidth=0.6pt, nodesep=3pt, rowsep=0.6cm, colsep = 1cm}
\everypsbox{\scriptstyle}
\begin{psmatrix}
%%% nodes
X'' & X' & X \\%
S'' & S' & S
%%% horizontal arrows
\ncline{1,1}{1,2}\naput{g'} \ncline{1,2}{1,3}\naput{g}
\ncline{2,1}{2,2}\nbput{f'} \ncline{2,2}{2,3}\nbput{f}
%%% vertical arrows
\ncline{1,1}{2,1} \ncline{1,2}{2,2}\ncline{1,3}{2,3}
\ncline[linestyle =none, arrows=-]{1,2}{2,3}\ncput{\textstyle\square}
\end{psmatrix}
\]
\vskip 1cm
\texttt{tikz-cd solution: }
\[ \begin{tikzcd}[arrows={-Stealth}]
X''\rar["g'"]\dar & X'\rar["g"]\dar\drar[phantom, "\square"] & X\dar \\%
S''\rar[swap, "f'"] & S'\rar[swap, "f"] & S
\end{tikzcd}
\]
\end{document}