In this paper we shall be mainly concerned with groups which can be covered by (in other words, are unions of) permutable boundedly finite subsets. Obvious examples of such groups are the finite groups, where a single finite set suffices, namely the group itself; and abelian groups, where all one-element subsets will serve. The main result (Theorem 7.1) characterizes these groups completely as ...

We investigate the hardness of approximating a transshipment problem with a permutable transit vector. We have already known that the transshipment problem of minimizing the total shipping cost is NP-hard. In this paper, we prove that even if the unit shipping cost associated with every arc is given as a positive integer, there is no polynomial time constant factor approximation algorithm for t...

Let σ = {σi|i ∈ I } be a partition of the set all primes ℙ and G finite group. A ℋ subgroups is said to complete Hall σ-set if every member ≠1 σi-subgroup for some i contains exactly one such that σi ⌒ π(G) ≠ ∅. group σ-primary it σi-group i. subgroup be: σ-permutable in possesses AH x H xA G; σ-subnormal there chain A0 ≤ A1 … At either Ai − 1 ⊴ or /(Ai 1)Ai 1, …, t;