(Named after the British mathematiCian Bertrand Russell (1872-1970)). Wm. Leler. Rule-based speCifiCation language based on augmented term rewriting. Used to implement Constraint languages. The user must expliCitly speCify the tree-searCh and the Constraint propagation. . ["Constraint Programming Languages - Their SpeCifiCation and Generation", W. Leler, A-W 1988, ISBN 0-201-06243-7].