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GHP formalism
The GHP formalism (or Geroch–Held–Penrose formalism) is a technique used in the mathematics of general relativity that involves singling out a pair of null directions at each point of spacetime.
See also
General relativity
NP formalism
References
Geroch, Robert, Held, A. and Penrose, Roger. "A space-time calculus based on pairs of null directions". JMP. Retrieved February 19, 2005.
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