Hamish Ivey-Law hlaw at iml.univ-mrs.fr
Tue Jan 19 14:53:27 CET 2010

Dear xy-pic list,

I am trying to typeset a diagram which has two entries.  There is a
large entry which is above a small entry, and I would like to have
multiple arrows from the small entry underneath to different parts of
the large entry above.  For example, I might have:

\xymatrix{
{A \times B \times C} \\
{X} \ar[u] \ar[u]
}

and I would like the first \ar[u] to point towards  A  and the second
to point towards  C.  Of course, I'd rather avoid splitting the large
entry into multiple entries as that tends to wreak havoc with the
typesetting, so I'm looking for a way to shift the head of the \ar[u]
to the left or right so that it points to the right bit.

Please forgive me if this is a simple question.  I read enough of the
reference manual to suspect that the answer involves the use of the
vector objects, but try as I might I couldn't get their syntax
correct.