Outer automorphism groups of ordered permutation groups

by Droste and Shelah. [DrSh:743]
Forum Math, 2002
An infinite linearly ordered set (S, <=) is called doubly homogeneous if its automorphism group A(S) acts 2-transitively on it. We show that any group G arises as outer automorphism group G cong Out (A(S)) of the automorphism group A(S), for some doubly homogeneous chain (S, <=) .

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