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Abstract Let 𝐺 be a group. A subgroup 𝐻 of 𝐺 is called permutable if H X = X H HX=XH for all subgroups 𝑋 of 𝐺. Permutability is not in general a transitive relation, and 𝐺 is called a PT PT -group if, whenever 𝐾 is a permutable subgroup of 𝐺 and 𝐻 is a permutable subgroup of 𝐾, we always have that 𝐻 is permutable in 𝐺. The property PT PT is not inherited by subgroups, and 𝐺 is called a PT ̄ PT -group if all its subgroups have the PT PT -property. We prove that if 𝐺 is a soluble group of infinite rank whose proper subgroups of infinite rank have the PT PT -property, then 𝐺 is a PT ̄ PT -group.
Ballester‐Bolinches et al. (Thu,) studied this question.