On $$ {\varSigma}_t^{\sigma } $$ -Closed Classes of Finite Groups

All analyzed groups are finite. Let σ = {σi| i ∈ I} be a partition of the set of all primes ℙ. If n is an integer, then the symbol σ(n) denotes a set {σi| σi ∩ π(n) ≠ ∅}. The integers n and m are called σ -coprime if σ(n) ∩ σ(m) =  ∅ . Let t > 1 be a natural number and let 𝔉 be a class of groups. Then we say that 𝔉 is null null null null null null null null null null null null null null null null null null null null null null null null null...