  We introduce a quantum loop group associated to a general symmetric Cartan
matrix, by imposing just enough relations between the usual generators
$\{e_{i,k}, f_{i,k}\}_{i \in I, k \in \mathbb{Z}}$ in order for the natural
Hopf pairing between the positive and negative halves of the quantum loop group
to be perfect. As an application, we describe the localized K-theoretic Hall
algebra of any quiver without loops, endowed with a particularly important
$\mathbb{C}^*$ action.
