  We define wreath products of cocommutative Hopf algebras, and show that they
enjoy a universal property of classifying cleft extensions, analogous to the
Kaloujnine-Krasner theorem for groups.
  We show that the group ring of a wreath product of groups is the wreath
product of their group rings, and that (with a natural definition of wreath
products of Lie algebras) the universal enveloping algebra of a wreath product
of Lie algebras is the wreath product of their enveloping algebras.
  We recover the aforementioned result that group extensions may be classified
as certain subgroups of a wreath product, and that Lie algebra extensions may
also be classified as certain subalgebras of a wreath product.
