Two-dimensional convexities are join-hull commutative |
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Authors: | M Van De Vel |
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Institution: | Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands |
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Abstract: | It is shown that two-dimensional convex structures with certain natural properties are join-hull commutative. The main intermediate step is the computation of the so-called exchange number. We also give two examples of three-dimensional convexities which are not join-hull commutative. The second one has certain additional properties showing that the main theorem is sharp in many other respects. These properties are obtained from a study of convex hyperspaces. |
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Keywords: | Primary 52A35 54H99 Secondary 54B20 54F45 |
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