Boundary control theory for hyperbolic and parabolic partial differential equations with constant coefficients Walter Littman (1978) Annali della Scuola Normale Superiore di Pisa - Classe di Scienze
Boundary controllability of hyperbolic equations. Èmanuilov, O.Yu. (2000) Sibirskij Matematicheskij Zhurnal
Boundary value problems for partial differential equations with piecewise constant delay. Wiener, Joseph (1991) International Journal of Mathematics and Mathematical Sciences