Let L1(G) and M(G) be the group algebra and the measure algebra of a locally compact group G 2 [SIN], respectively, and ∆ : L1(G) ! M(G) be a continuous linear map behaving like derivation at two-sided orthogonality conditions f ∗ g = g ∗ f = 0 or f ∗ g? = g? ∗ f = 0. We describe ∆ in terms of derivations.
