H. Macpherson. (2019)cite arxiv:1910.13380Comment: PhD Thesis, 174 pages, 23 figures, contains versions of the articles arXiv:1611.05447, arXiv:1807.01711, and arXiv:1807.01714.
A. Coley, and G. Ellis. (2019)cite arxiv:1909.05346Comment: To appear as Topical Review in Class. Quant. Grav. arXiv admin note: text overlap with arXiv:1809.04926 by other authors.