# [Xy-pic] loop in xy-pic

Thierry Coquand coquand@cs.chalmers.se
Tue, 22 Oct 2002 17:15:18 +0200 (MET DST)

 I have just started to use xy-pic for drawing some simple
finite-state automata

The following example was simple to write and produce what
is expected

\newcommand\putc[1]{*++[o][F-]{#1}}

$\xymatrix{ \putc{A} \ar@/_1pc/[rr]_{\lambda} \ar@/_1pc/[dd]_{\alpha} & & \putc{B} \ar@/_1pc/[ll]_{\mu} \\ \\ \putc{C} \ar@/_1pc/[rr]_{\epsilon} & & *++[o][F=]{D} \ar@/_1pc/[uu]_{\gamma} }$

I would like now to add a loop from the edge D to itself.
The following change is not accepted

$\xymatrix{ \putc{A} \ar@/_1pc/[rr]_{\lambda} \ar@/_1pc/[dd]_{\alpha} & & \putc{B} \ar@/_1pc/[ll]_{\mu} \\ \\ \putc{C} \ar@/_1pc/[rr]_{\epsilon} & & *++[o][F=]{D} \ar@/_1pc/[uu]_{\gamma} \ar@(r,d)[]^{b} }$

Is there a simple way to modify the previous diagram with a
loop from D to itself??