Injective subsets of l∞(I)

We prove an explicit characterization of all injective subsets of the model space l∞(I) of all bounded real-valued functions defined on a non-empty set I, endowed with the supremum norm. Since the class of all injective metric spaces coincides with the one of all absolute 1-Lipschitz retracts, the present work yields a characterization of all the subsets of l∞(I) that are absolute 1-Lipschitz retracts.