On a problem of the theory of multiply local formations.
New criteria of existence and conjugacy of Hall subgroups of finite groups are given.
A class ℱ of universal algebras is called a formation if the following conditions are satisfied: 1) Any homomorphic image of A ∈ ℱ is in ℱ; 2) If α₁, α₂ are congruences on A and , i = 1,2, then A/(α₁∩α₂) ∈ ℱ. We prove that any formation generated by a simple algebra with permutable congruences is minimal, and hence any formation containing a simple algebra, with permutable congruences, contains a minimum subformation. This result gives a partial answer to an open problem of Shemetkov and Skiba...
Let be some partition of the set of all primes , be a finite group and . A set of subgroups of is said to be a complete Hall -set of if every non-identity member of is a Hall -subgroup of and contains exactly one Hall -subgroup of for every . is said to be -full if possesses a complete Hall -set. A subgroup of is -permutable in if possesses a complete Hall -set such that = for all and all . A subgroup of is -permutably embedded in if is -full...
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