Benchmark proposal: 18-player mixed-size tee-time rotation

Hello GroupMixer team, Would you be interested in an additional constrained benchmark case based on a four-round golf rotation with a proven fairness optimum? The case has 18 players and five ordered groups per round, with exact sizes (3,3,4,4,4). The same size pattern repeats in every round. Groups correspond to tee slots at 10:00, 10:07, 10:14, 10:21 and 10:28. Every player attends every round, no unordered pair meets more than once, and four-player-group participation is balanced: six players have two four-player rounds and twelve have three, without prescribing identities. The objective lexicographically maximizes (1) the minimum number of distinct tee slots received by any player, then (2) total distinct slots across players. The proven optimum is (minimum 3, total 65), equivalently score 284 for 73 × minimum + total. We provide a validated reference schedule and an exhaustive symmetry-based exclusion of every improvement, independently checked in two OR-Tools formulations. Five additional fresh, no-hint local runs, seeds 101/202/303/404/505, each found (3,65) within a 60-second end-to-end deadline. Those attempts reported FEASIBLE, not solver-proven OPTIMAL; optimality comes from the separate exhaustive argument. Local ARM64/macOS timings are not a direct comparison with your benchmark: CPUs were not pinned and an 8 GiB process limit was not imposed. Public evidence: - [Case definition](https://github.com/jgojnich-a11y/enhanced-social-golfer-problem/blob/main/N18_BENCHMARK_CASE.md) - [Reference schedule](https://github.com/jgojnich-a11y/enhanced-social-golfer-problem/blob/main/solutions/optimal/n18_sol.csv) - [Optimality proof and audit](https://github.com/jgojnich-a11y/enhanced-social-golfer-problem/tree/main/runs/n18_canonical_two_rounds_20261003) - [Fresh no-hint benchmark evidence](https://github.com/jgojnich-a11y/enhanced-social-golfer-problem/tree/main/runs/n18_cold_benchmark_20261003) The reference schedule and optimum are evaluation evidence, not embedded answers or hints for a benchmarked solver. Does this fit your benchmark scope, and can your scenario format express the exact lexicographic tee-slot objective and group-size participation balance? If so, what format would you prefer for contributing the case? John Gojnich