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Ideas for 'The Evolution of Logic', 'Theory of Good and Evil' and 'The Foundations of Mathematics (2nd ed)'

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6. Mathematics / B. Foundations for Mathematics / 3. Axioms for Geometry

13474	Euclid has a unique parallel, spherical geometry has none, and saddle geometry has several [Hart,WD]
	Full Idea: There is a familiar comparison between Euclid (unique parallel) and 'spherical' geometry (no parallel) and 'saddle' geometry (several parallels).
	From: William D. Hart (The Evolution of Logic [2010], 2)