“…In the same paper, the authors also investigate similar problems for other group invariants, such as π(G) (the set of prime divisors of |G|), ω(G) (the set of orders of elements of G), exp(G) (the exponent of G), etc. For example, [14,Theorem A] implies that every finite group G has a 2-generated subgroup H such that π(G) = π(H), and appropriate extensions to profinite groups have recently been established by Covato [5].…”