Adding boxed texts on commutative diagram

Question

I'm trying to draw this commutative diagram (source: Elements of Algebraic Topology by James Munkres). I know how to draw the diagram using tikzcd without the boxes. Can someone help me about how to add these boxes on the tikzcd diagram?

Answer 1

We can place the boxes in the middle as labels “near end”, but a bit lowered and with smashed depth. For the upper boxes, I use \overset, but making the boxes zero width for safety.

\documentclass{article}
\usepackage{amsmath}
\usepackage{tikz-cd}

\newcommand{\sboxed}[1]{%
  \,\raisebox{-1ex}[\height][0pt]{\fbox{$\scriptstyle\mathstrut#1$}}%
}
\newcommand{\uboxed}[1]{%
  \makebox[0pt]{\fbox{$\scriptstyle\mathstrut#1$}}%
}

\begin{document}

\begin{tikzcd}[row sep=huge,column sep=large]
0 \arrow[r] &
C_{p+1} \arrow[r,"\phi"] \arrow[d,"\partial_C"',"\sboxed{c_p}" near end] &
\overset{\uboxed{d_{p+1}}}{D_{p+1}}
  \arrow[r,"\psi"] \arrow[d,"\partial_D"',"\sboxed{d_p}" near end] &
\overset{\uboxed{e_{p+1}}}{E_{p+1}}
  \arrow[r] \arrow[d,"\partial_E"',"\sboxed{e_p}" near end] &
0 \\
0 \arrow[r] &
C_{p} \arrow[r,"\phi"] \arrow[d,"\partial_C"',"\sboxed{c_{p-1}}" near end] &
D_{p} \arrow[r,"\psi"] \arrow[d,"\partial_D"',] &
E_{p} \arrow[r] \arrow[d,"\partial_E"'] &
0 \\
0 \arrow[r] &
C_{p-1} \arrow[r,"\phi"] &
D_{p-1} \arrow[r,"\psi"] &
E_{p-1} \arrow[r] &
0
\end{tikzcd}

\end{document}