Whitehead, A. N. (1927). Principia mathematica: To 56. C.U.Pr.
Tohutoru Kātū Chicago (17th ed.)Whitehead, Alfred North. Principia Mathematica: To 56. Cambridge: C.U.Pr, 1927.
Tohutoro MLA (9th ed.)Whitehead, Alfred North. Principia Mathematica: To 56. C.U.Pr, 1927.
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