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单词 SchreierIndexFormula
释义

Schreier index formula


Let F be a free groupMathworldPlanetmath of finite rank, and let H be a subgroupMathworldPlanetmathPlanetmath (http://planetmath.org/Subgroup) of finite index in F.By the Nielsen-Schreier theorem, H is free.The Schreier index formula states that

rank(H)=|F:H|(rank(F)-1)+1.

This implies more generally that if G is a group generated by m elements, then any subgroup of index n in G can be generated by at most nm-n+1 elements.

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更新时间:2025/5/5 1:15:50