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Three-colouring arrangements of great circles
Prove that the crossing points of every simple arrangement of great circles can be 3-coloured, or find one that needs four colours.
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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