X RAY BACKGROUND: General: de Zotti et al. 93/02; Giommi et al. 98/12; Fabian 2000/01; Gilli 2003/03; Re: ACTIVE GALACTIC NUCLEI: Giommi et al. 98/12; Comastri 98/12; Almaini 2000/01; Fabian 2000/01; Re: GALACTIC EVOLUTION: Fabian 2000/01; THE NET ADVANCE OF PHYSICS
X RAY BACKGROUND: