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Hunter Liu (talk | contribs) →Proof in the Beltrami-Klein model: add another method of construction |
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Alternatively, we can construct the common perpendicular of the ultraparallel lines as follows: the ultraparallel lines in Beltrami-Klein model are two non-intersecting chords. But they actually intersect outside the circle. The polar of the intersecting point is the desired common perpendicular.<ref>W. Thurston, Three-Dimensional Geometry and Topology, p72</ref>
==References==
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