RU-ALLRUSSIAN 1975 Problem 10
The finite sequence has each member 0, 1 or 2. A move involves replacing any two unequal members of the sequence by a single member different from either. A series of moves results in a single number. Prove that no series of moves can terminate in a (single) different number.
Dataset text NuminaMath olympiads. Quoted with source.
Solutions
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