  The arising of central extensions is discussed in two contexts. At first
classical counterparts of quantum anomalies (deserving being named as
"classical anomalies") are associated with a peculiar subclass of the
non-equivariant maps. Further, the notion of "residual symmetry" for theories
formulated in given non-vanishing EM backgrounds is introduced. It is pointed
out that this is a Lie-algebraic, model-independent, concept.
