2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/63629This note provides a simple result showing, under suitable technical assumptions, that if a system S adapts to a class of external signals U, then S must necessarily contain a subsystem which is capable of generating all the signals in U. It is not assumed that regulation is robust, nor is there a prior requirement for the system to be partitioned into separate plant and controller components.Further work in http://math.rutgers.edu/~sontagOptimization and ControlDynamical Systems93B99;93C15text