Coproduct for Yangians of affine Kac-Moody algebras

Given an affine Kac-Moody algebra, we explain how to construct a coproduct on its associated Yangian. In order to prove that this coproduct is an algebra homomorphism, we obtain, in the first half of this paper, a minimalistic presentation of the Yangian when the Kac-Moody algebra is, more generally, symmetrizable.