We present three examples of countable homogeneous structures (also called Fraïssé limits) whose automorphism groups are not universal, namely, fail to contain isomorphic copies of all automorphism groups of their substructures.Our first example is a particular case of a rather general construction on Fraïssé classes, which we call diversification, leading to automorphism groups containing copies of all finite groups. Our second example is a special case of another general construction on Fraïssé classes, the mixed sums, leading to a Fraïssé class with all finite symmetric groups appearing as automorphism groups and at the same time with a torsion-free automorphism group of its Fraïssé limit. Our last example is a Fraïssé class of finite models with arbitrarily large finite abelian automorphism groups, such that the automorphism group of its Fraïssé limit is again torsion-free.

中文翻译：

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具有非全自同态群的同构结构

我们提出了三个可数同质结构的例子（也称为弗雷塞限制) 的自同构群不是普遍的，即不包含其子结构的所有自同构群的同构副本。我们的第一个例子是在 Fraïssé 类上相当普遍的构造的一个特例，我们称之为多样化，导致自同构群包含所有有限群的副本。我们的第二个例子是另一个关于 Fraïssé 类的一般构造的特例，混合金额，导致所有有限对称群都显示为自同构群的 Fraïssé 类，同时具有其 Fraïssé 极限的无扭转自同构群。我们的最后一个例子是具有任意大的有限阿贝尔自同构群的有限模型的 Fraïssé 类，因此其 Fraïssé 极限的自同构群又是无扭转的。