1. Department of Pure Mathematics, University of Waterloo, 200 University Ave. West, Waterloo, ON, Canada N2L 3G1. jockusch@math.uiuc.edu
2. Department of Mathematics, University of Connecticut, 341 Mansfield Road U1009, Storrs, CT, 06269, U.S.A.. david.solomon@uconn.edu
3. Department of Mathematics, University of Chicago, 5734 S. University Ave., Chicago, IL, 60637, U.S.A.. linda.westrick@uconn.edu
4. Department of Mathematics, University of Illinois, 1409 W. Green Street, Urbana, IL, 60801, U.S.A.. jockusch@math.uiuc.edu
5. Department of Mathematics, University of Connecticut, 341 Mansfield Road U1009, Storrs, CT, 06269, U.S.A.. linda.westrick@uconn.edu