2

Consider the tex:

\xymatrix{
    M \ar[r]^{f}\ar[d]_{h} & N \ar@{-->}[dl]^{g} \\
     P}

If f is isomorphism, not identity. How to change the tex? If I replace \ar[r]^{f} by \ar@{\cong }[r]^{f}, this can't work. How to get isomorphism?

  • 1
    (1) welcome, (2) as always on this site you are much much more likely to get help if you provide a full minimal example others can copy and test as is. – daleif Jan 31 at 14:06
3

The usual way would be to add \cong under the arrow:

Sample output

\documentclass{article}

\usepackage[all]{xy}

\begin{document}

\xymatrix{
    M \ar[r]^{f}_{\cong} \ar[d]_{h} & N \ar@{-->}[dl]^{g} \\
     P}

\end{document}

The \ar@... syntax tries to change the arrow type, but there is not really a standard arrow symbol for isomorphism.

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