Arrows in xy-pic have narrow heads, but I need heavy tips for my graphs. I tried the follwoing arrow definition, but the tip of the arrow enters into the circle of graph node.
\documentclass{report}
\usepackage[all]{xy}
\newdir{|>}{%
!/4.5pt/@{|}*:(1,-.2)@^{>}*:(1,+.2)@_{>}}
\begin{document}
\[
\xygraph{
!{<0cm,0cm>;<2cm,0cm>:<0cm,2cm>::}
!{(0,0)}*+=[o]+[F]{1}="1"
!{(1,0)}*+=[o]+[F]{2}="2"
"1":@{|>}"2"
}
\]
\end{document}
Would you please help me to avoid this problem?
How can I fill insdie the arrow tip? Or preferably get something like: 
