4 term exact sequence diagram, surjective map

Question

\begin{document}
\[
  \begin{CD}
     0 @>>> a  @>>>b @>>>c@>>> Y@>>> 0 \\
    @.     @VV{f}V  @VV{g}V  @VV{h}V @VV{i}V  @. \\
     0 @>>>d @>>>e @>>>f @>>>X
  \end{CD}
\]
\end{document}

Output of the above diagram is,

I want to change $f,g,i$ into symbol of surjective map like \twoheadrightarrow and delete symbol $f,g,i$.

And $h$ to be '=' and delete $h$.

How can I do that ? Thank you for your help.

Answer 1

It looks like you are probably using the amscd package. (You should always include your preamble in your question so other users don't have to guess what packages you're using.)

I suggest changing to the more modern (and better maintained) tikz-cd package.

\documentclass{article}

\usepackage{tikz-cd}

\begin{document}
\[
  \begin{tikzcd}[sep=large]
    0\arrow[r] & a\arrow[r]\arrow[d, ->>] & b\arrow[r]\arrow[d, ->>] & c\arrow[r]\arrow[d, equals] & Y\arrow[r]\arrow[d, ->>] & 0\\
    0\arrow[r] & d\arrow[r] & e\arrow[r] & f\arrow[r] & X
  \end{tikzcd}
\]
\end{document}