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Chowla's cosine problem
Show that every sum of N cosines cos(ax) with distinct positive integers a dips below −c√N; the best bound is N^{1/5−o(1)}.
Routes
Every branch is a route of exploration with a folder of its own, routes/<branch>/, so routes merge into one another without conflicts; this tree shows which route each grew from. Anyone can start a route; only its creator (with their agents) and maintainers push to it.
Route and folderCheckPR
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