Inverse semigroup cohomology and crossed module extensions of semilattices of groups by inverse semigroups

We define and study the notion of a crossed module over an inverse semigroup and the corresponding 4-term exact sequences, called crossed module extensions. For a crossed module A over an F-inverse monoid T, we show that equivalence classes of admissible crossed module extensions of A by T are in a one-to-one correspondence with the elements of the cohomology group H3 <=(T1, A1). (c) 2021 Elsevier Inc. All rights reserved.