1. The seventeenth-century doctrine of a plurality of worlds
2. Aristotle, nd. De Caelo, v1: p 5-9..
3. Plato, nd. Time, v 31:55.
4. An explanation for the absence of extraterrestrials on earth;Hart;Q. J. Roy. Astron. Soc.,1975
5. An explanation for the absence of extraterrestrials on earth – correspondence;Cox;Q. J. Roy. Astron. Soc.,1976