Inside a certain definition, I want to create a condition on the existence of
an undefined label: I want to say something like:
if \refn{#1} is undefined (i.e., if #1 is an undefined label), then...
else...
fi
. How can I write that? I tried with `\ifx\refn{#1}\empty...' but doesn't
work.
Thanks indeed for any help
Rodolfo