Abstract
An automorphism of an arbitrary group is called normal if all subgroups of this group are left invariant by it. Lubotski [1] and Lue [2] showed that every normal automorphism of a noncyclic free group is inner. Here we prove that every normal automorphism of a nontrivial free product of groups is inner as well.
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References
A. Lubotski, “Normal automorphisms of free groups,”J. Alg.,63, No. 2, 494–498 (1980).
A. S.-T. Lue, “Normal automorphisms of free groups,”J. Alg.,64, No. 1, 52–53 (1980).
R. Lyndon and P. Schupp,Combinatorial Group Theory, Springer, New York (1977).
M. I. Kargapolov and Yu. I. Merzlyakov,Foundations of Group Theory [in Russian], Nauka, Moscow (1982).
Additional information
Supported by RFFR grant No. 13-011-1513.
Translated fromAlgebra i Logika, Vol. 35, No. 5, pp. 562–566, September–October, 1996.
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Neshadim, M.V. Free products of groups have no outer normal automorphisms. Algebr Logic 35, 316–318 (1996). https://doi.org/10.1007/BF02367356
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DOI: https://doi.org/10.1007/BF02367356