Some ancestors of contraction analysis

Contraction analysis is a recent tool for analyzing the convergence behavior of nonlinear systems in state-space form (see Lohmiller and Slotine [16] for the main reference). However, it seems that earlier results derived by mathematicians in the 1950s closely match some of the results of contraction analysis. In this paper, we review and place into perspective some references of this era, and relate them with contraction.