Solutions of the d'Alembert equation in ?n -- Solutions of the d'Alembert equation in arbitrary domains -- Steady-state scattering theory in exterior domains and the limiting absorption principle -- Time-dependent scattering theory in exterior domains -- Steady-state scattering theory and eigenfunction expansions for A -- Wave operators and asymptotic solutions of the d'Alembert equation in exterior domains -- Asymptotic wave functions and energy distributions in exterior domains