Let (S, +) be a semigroup and (H, +) be a group (neither necessarily commutative). Suppose that J ⊂ 2s is a proper ideal in S such that
![](//static.cambridge.org/content/id/urn%3Acambridge.org%3Aid%3Aarticle%3AS0004972700017743/resource/name/S0004972700017743_eqnU1.gif?pub-status=live)
and Ω(J) = {M ⊂ S2 : there exists U(M)∈ J with M [x] ∈ J for x ∈ S/U(M)}, where M[x] = {y ∈ S : (y, x) ∈ M}. We show that if f : S → H is a function satisfying
![](//static.cambridge.org/content/id/urn%3Acambridge.org%3Aid%3Aarticle%3AS0004972700017743/resource/name/S0004972700017743_eqnU2.gif?pub-status=live)
then there exists exactly one additive function F : S → H with F(x) = f(x) J-almost everywhere in S.
We also prove some results concerning regularity of the function F.