Pigeonhole and extremal problems
Coloured beads and balloons 18Coprime subsets 12🔒Divisibility chains 18🔒Extremal counting 17🔒Families of sets 12🔒Forcing a sum condition 14🔒Guaranteed minimum 18🔒Maximum sums in sequences 18🔒Pairs and the pigeonhole principle 13🔒Parity arrangements 6🔒Ramsey-type colourings 7🔒Smallest sums of sets 11🔒Subsets avoiding differences 13🔒