References (voce: Relatività generale, soluzioni della); ; WMWWolfram MathWorld. A free resource from Wolfram Research built with Mathematica technology, created, developed and nurtured by Eric Weisstein with contributions from the World's mathematical community
; Wikipedia(IT)Wikipedia. L'enciclopedia libera, 2001 [ed. in lingua italiana dell' enciclopedia online Wikipedia]
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