Busby, Jason. Mastering unreal technology : The act of level design/ Jason Busby, Zak Parrish, Joel Van Eenwyk. - USA: Sams Publishing. 2005. - xvii, 962p. ill. 23 cm. ISBN: 9780672326929 0672326922 LC Class. No.: Q76.76.C672 / .B96 2005