Mentioned in Attribute Grammars, LNCS 323, p.108.

Relational Language. Clark & Gregory. First parallel logic language to use the concept of committed choice. Forerunner of PARLOG. "A Relational Language for Parallel Programming", K.L. Clark et al, Proc ACM Conf on Functional Prog Langs and Comp Arch, pp.171-178, ACM 1981.