Closed and Open Forms
It is important to distinguish two different forms of the quartic. The closed quartic is what is generally meant in geometry; topologically it has genus 3 and is a compact space. The open or "punctured" quartic is of interest in number theory; topologically it is a genus 3 surface with 24 punctures, and geometrically these punctures are cusps. The open quartic may be obtained (topologically) from the closed quartic by puncturing at the 24 centers of the tiling by regular heptagons, as discussed below. The open and closed quartics have different metrics, though they are both hyperbolic and complete – geometrically, the cusps are "points at infinity", not holes, hence the open quartic is still complete, because these points cannot be reached.
Read more about this topic: Klein Quartic
Famous quotes containing the words closed, open and/or forms:
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Pawnbroker: Sure they are. It’s Yom Kippur.
Don: It’s what?
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—Billy Wilder (b. 1906)
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—Eric Hoffer (1902–1983)