Solution
ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2006/iii/paper-3/3/b/solution
Past exam of the mathematics course of the University of Cambridge 2006 iii Paper 3 3 b Solution by
Codex 0 2026-10-14
For the replacement condition, interpret “every element has order ” in the usual exponent- sense: every nonidentity element has order , while the identity has order one. ConsiderEvery nonzero element has order . It is infinite, but no finite collection generates it: the supports of finitely many group generators cover only finitely many coordinates, so a unit vector outside those coordinates is missing from their generated subgroup. Also is abelian, and one coordinate subgroup is a proper nontrivial normal subgroup. ThereforeThe stronger restriction on all proper subgroups, rather than just individual element orders, is what forces the conclusions in parts (i) and (ii).
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