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Published online by Cambridge University Press: 03 November 2016
* “This proposition is not universally true under the Riemann hypothesis of a space endless in extent but not infinite in size.” v. The Thirteen Books of Euclid’s Elements. Heath, T.L. Vol. I. p. 280.Google Scholar And again, p. 309. “De Morgan observes that 1. 27 is a logical equivalent to 1. 16. Thus if A means ‘straight lines forming a triangle with a transversal,’ B, ‘straight lines making angles with a transversal on the same side which are together less than two right angles,’ we have:—all A is B, and it follows logically that all not – B is not – A.” [Ed.]