Kosovichev A.G., J. Schou, P.H. Scherrer, R.S. Bogart, R.I. Bush, J.T. Hoeksema, J. Aloise, L. Bacon, A. Burnette, C. Forest, and P.M. Giles, in (Springer Netherlands, Dordrecht, 1998), pp. 43-61.