1. P.A.R. Ade et al. [Planck Collaboration], Planck 2013 results. XXVI. Background geometry and topology of the Universe. A&A 571, A26 (2014). arXiv:1303.5086 [astro-ph.CO]
2. J.-P. Luminet, The shape and topology of the Universe. arXiv:0802.2236 [astro-ph]
3. B.F. Roukema, Topology of the Universe: background and recent observational approaches. Pramana 53, 945 (1999). arXiv:astro-ph/9904113
4. W. Piechocki, Topology of the Universe. arXiv:gr-qc/9910055
5. P. Bielewicz, A. Riazuelo, The study of topology of the universe using multipole vectors. Mon. Not. R. Astron. Soc. 396, 609 (2009). arXiv:0804.2437 [astro-ph]