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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.
a term used to denote the set of geometrical propositions which are independent of the postulate about parallel lines—that is, common to Euclidean and Lobachevskii geometry.
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.