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Plane Geometry - Bruce E. Shapiro

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34 SECTION 8. HILBERT’S AXIOMSiom of continuity introduces the continuity of real numbers to geometry,and completeness tells us that everything we can possibly know we canlearn from these axioms.Hilbert’s Axioms of Connection1. Two distinct points A and B always completely determine a straight line a. We writeAB = a or BA = a.2. Any two distinct points of a straight line completely determine that line; that is, ifAB = a and AC = a, where B ≠ C, then also BC = a.3. Three points A, B, C not situated in the same straight line always completely determineaplane α. We write ABC = α.4. Any three points A, B, C of a plane α, which do not lie in the same straightline,completely determine that plane.5. If two points A, B of a straight line a lie in a plane α, then every point of a lies in α.6. If two planes α, β have a point A in common, then they have at least a second pointB in common.7. Upon every straight line there exist at least two points, in every plane at least threepoints not lying in the same straight line, and in space there exist at least four pointsnot lying in a plane.Hilbert’s Axioms of Order1. If A, B, C are points of a straight line and B lies between A and C, then B lies alsobetween C and A.2. If A and C are two points of a straight line, then there exists at least one point Blying between A and C and at least one point D so situated that C lies between Aand D.3. Of any three points situated on a straight line, there is always one and only one whichlies between the other two.4. Any four points A, B, C, D of a straight line can always be so arranged that B shalllie between A and C and also between A and D, and, furthermore, that C shallliebetween A and D and also between B and D.5. Let A, B, C be three points not lying in the same straight line and let a be a straightline lying in the plane ABC and not passing through any of the points A, B, C.Then, if the straight line a passes through a point of the segment AB, it will alsopass through either a point of the segment BC or a point of the segment AC.Hilbert’s Axiom of ParallelsIn a plane α there can be drawn through any point A, lying outside of a straight line a, oneand only one straight line which does not intersect the line a. This straight line is called theparallel to a through the given point A.« CC BY-NC-ND 3.0. Revised: 18 Nov 2012

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