D. Bak. (2006)cite arxiv:hep-th/0603080
Comment: 18 pages, 5 figures, references added, minor corrections, further
minor corrections, v4: some clarification and more details added.
B. Craps, T. Hertog, and N. Turok. (2007)cite arxiv:0712.4180
Comment: 91 pages, 24 figures; minor reorganization of introduction,
clarifying comments throughout.
G. Horowitz, A. Lawrence, and E. Silverstein. (2009)cite arxiv:0904.3922
Comment: 30 pages, 4 figures. v2: typos fixed, references and acknowledgements
added, a few small changes in the text.