•Suppose *P* is the
nominal model and* K* is a controller.

•**Nominal Stability (NS):** if *K* stabilizes the nominal *P*.

•**Robust Stability (RS):** if *K* stabilizes every plant in **P**.

•**Nominal Performance (NP):** if the performance objectives are
satisfied for the nominal plant *P.*

•**Robust Performance(RP):** if the performance objectives are
satisfied for every plant in **P**.