| Popis: |
Let fd(n), n > d ≥ 2, be the smallest positive integer such that any set of fd(n) points, in general position in Rd, contains n points in convex position. Let hd(n, k), n > d ≥ 2 and k ≥ 0, denote the smallest number with the property that in any set of hd(n, k) points, in general position in Rd, there are n points in convex position whose convex hull contains at most k other points. Previous result of Valtr states that h4(n, 0) does not exist for all n ≥ 249. We show that h4(n, 0) does not exist for all n ≥ 137. We show that h3(8, k) ≤ f3(8) for all k ≥ 26, h4(10, k) ≤ f4(10) for all k ≥ 147 and h5(12, k) ≤ f5(12) for all k ≥ 999. Next, let fd(k, n) be the smallest number such that in every set of fd(k, n) points, in general position in Rd, there are n points whose convex hull has at least k vertices. We show that, for arbitrary integers n ≥ k ≥ d + 1, d ≥ 2, fd(k, n) ≥ (n − 1) (k − 1)/(cd logd−2 (n − 1)), where cd > 0 is a constant dependent only on the dimension d. 1 |
