L #@- L1, ..., Ln
or
- L1, ..., Ln
where n=0. If L is false the clause is regarded as a goal.
The name "Horn Clause" comes from the logician Alfred Horn,
who first pointed out the significance of such clauses in
1951, in the article "On sentences which are true of direct
unions of algebras", Journal of Symbolic Logic, 16, 14-21.
positive literal.
(2000-01-24)