|HiLog - A higher-order logic programming language. An extension of
normal logic programming where predicate symbols may be
variable or structured. This allows unification to be
performed on the predicate symbols themselves in addition to
["HiLog as a Platform for Database Languages (Or Why Predicate Calculus is Not Enough)", W. Chen et al, Stony Brook, 2nd Intl Workshop on Database Prog Langs, Morgan Kaufmann, 1989].