Geroch, Robert (1968), "Spinor Structure of Space-Times in General Relativity. I", Journal of Mathematical Physics, 9 (11): 1739–1743, Bibcode:1968JMP.....9.1739G, doi:10.1063/1.1664507
Parker, Phillip E. (1984), "On some theorems of Geroch and Stiefel", Journal of Mathematical Physics, 25 (3): 597–599, doi:10.1063/1.1665067
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Geroch, Robert (1968), "Spinor Structure of Space-Times in General Relativity. I", Journal of Mathematical Physics, 9 (11): 1739–1743, Bibcode:1968JMP.....9.1739G, doi:10.1063/1.1664507