  Vertex algebras formalize the subalgebra of holomorphic fields of a conformal
field theory. OPE-algebras were proposed as a generalization of vertex algebras
that formalizes the algebra of all fields of a conformal field theory. We prove
some basic results about them: The state-field correspondence is an OPE-algebra
isomorphism and Dong's lemma and the existence theorem hold for multiply local
OPE-algebras; locality implies skew-symmetry; if skew-symmetry holds then
duality implies locality for modules and they are equivalent for algebras. We
define modules over OPE-algebras.
