1. S. Coleman, Harvard preprint HUTP-88/A008.
2. S. Giddings and A. Strominger, Harvard preprints HUTP-88/A-6, HUTP-88/A036; T. Banks, Santa Cruz preprint SCIPP-88/09; I. Klebanov, L. Susskind and T. Banks SLAC preprint SLAC-PUB-R705.
3. S. Weinberg, The cosmological constant problem, University of Texas preprint UTTG-12-88.