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• Baumgarte, Thomas W.; Shapiro, Stuart L. (2010), Numerical Relativity: Solving Einstein's Equations on the Computer, New York: Cambridge University Press, ISBN 978-0-521-51407-1
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• http://en.wikipedia.org/wiki/Tetradic_Palatini_action
• https://en.wikipedia.org/wiki/Self-dual_Palatini_action
• https://en.wikipedia.org/wiki/Ashtekar_variables
• https://en.wikipedia.org/wiki/Levi-Civita_connection
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• Muxin Han, https://www.youtube.com/user/hamsyn/videos
• https://en.wikipedia.org/wiki/Interior_product
• 1984 Penrose, Rindler - Spinors and Space-Time