Boundary control of a symmetric hyperbolic system with nonlinear boundary conditions Póvoas, M. (1982) Portugaliae mathematica
Boundary control problem with an infinite number of variables. El-Saify, Hussain A. (2001) International Journal of Mathematics and Mathematical Sciences
Boundary sentinels with given sensitivity. Gisèle Massengo Mophou, Jean-Pierre Puel (2009) Revista Matemática Complutense