edited by W. L. Van der Poel and L. A. Maarssen. edited by L. B. Sand and F. A. Mumpton. edited by K. A. van der Hucht, and G. Vaiana. edited by R.P. van de Riet and W. Litwin. edited by L. Marton and C. Marton. edited by W. A. D. Anderson, John M. Kissane. edited by A. van der Laan and A.A. Winters. edited by E. L. Grove, A. J. Perkins. edited by J. H. L. Henson and A. Whelan. edited by J.K. van der Korst.