[Xy-pic] Loop arrows (help!)

[Sofia Tirabassi]

Dear XY:
I am an Italian student, ana I am just beginning to appreciate the power
of the package xy-pic. I am writing a paper about theory of categories and
I need to create a graphic rappresentaiton of a gruppoid. My problem is that
I cannot figure out how to create loop arrows. I read the manual but I could
not manage my problem. Could you please help me?
Thank you in advance for your aid,
looking forward for hearing of you
Sofia