Bertrand

Named for the British mathematician Bertrand Russell (1872-1970)

William Leler

A rule-based specification language based on augmented term rewriting. It has been used primarily to implement constraint languages. The user must explicitly specify the tree-search and the constraint propagation.

Constraint Programming Languages - Their Specification and Generation, William Leler, Addison-Wesley, 1988, ISBN 0-201-06243-7.