I am trying to use xy
package to draw some diagrams. So I use the command \usepackage{xy}
and I type a sample as follows:
\xymatrix{
A &*+[F]{\sum_{i=n}^m {i^2}} \\
& {\bullet} & D \ar[ul] }
But this fails with the error undefined control sequence \xymatrix
I don't understand why. Someone can help me?
{}
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