@misc{Grabowski_Piotr_Circle,
 author={Grabowski, Piotr and Callier, Frank M.},
 howpublished={online},
 publisher={Zielona Góra: Uniwersytet Zielonogórski},
 language={eng},
 title={Circle criterion and boundary control systems in factor form: Input-output approach},
 type={artykuł},
 keywords={infinite-dimensional control systems, semigroups, input-output relations},
}