  Classes of functions of several variables on arbitrary non-empty domains that
are closed under permutation of variables and addition of dummy variables are
characterized in terms of generalized constraints, and hereby Hellerstein's
Galois theory of functions and generalized constraints is extended to infinite
domains. Furthermore, classes of operations on arbitrary non-empty domains that
are closed under permutation of variables, addition of dummy variables and
composition are characterized in terms of clusters, and a Galois connection is
established between operations and clusters.
