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Whitehead's lemma : ウィキペディア英語版 | Whitehead's lemma : Whitehead's lemma is a technical result in abstract algebra used in algebraic K-theory. It states that a matrix of the form : is equivalent to the identity matrix by elementary transformations (that is, transvections): : Here, indicates a matrix whose diagonal block is and entry is . The name "Whitehead's lemma" also refers to the closely related result that the derived group of the stable general linear group is the group generated by elementary matrices. In symbols, :. This holds for the stable group (the direct limit of matrices of finite size) over any ring, but not in general for the unstable groups, even over a field. For instance for : one has: : where Alt(3) and Sym(3) denote the alternating resp. symmetric group on 3 letters. ==See also==
*Special linear group#Relations to other subgroups of GL(n,A)
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