Summary
It is shown that the outer automorphism group of a Coxeter groupW of finite rank is finite if the Coxeter graph contains no infinite bonds. A key step in the proof is to show that if the group is irreducible andΠ 1 andΠ 2 any two bases of the root system ofW, thenΠ 2 = ±ωΠ 1 for some ω εW. The proof of this latter fact employs some properties of the dominance order on the root system introduced by Brink and Howlett.
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Howlett, R.B., Rowley, P.J. & Taylor, D.E. On outer automorphism groups of coxeter groups. Manuscripta Math 93, 499–513 (1997). https://doi.org/10.1007/BF02677488
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DOI: https://doi.org/10.1007/BF02677488