2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/73646We present $c_0$--semigroup generation results for the free streaming operator with abstract boundary conditions. We recall some known results on the matter and establish a general theorem. We motivate our study with a lot of examples and show that our result applies to the physical cases of Maxwell boundary conditions in the kinetic theory of gases as well as to the non--local boundary conditions involved in transport--like equations from population dynamics.28 pagesAnalysis of PDEsMathematical Physicstext