Teacher:In this task, we ask you to elaborate the sentence without changing its general meaning. You can do so by explaining further the input sentence, using more precise wording, adding qualifiers and auxiliary information etc.
Teacher: Now, understand the problem? Solve this instance: A Horn clause with exactly one positive literal is a definite clause ; a definite clause with no negative literals is sometimes called a " fact " ; and a Horn clause without a positive literal is sometimes called a goal clause .
Student:
A Horn clause with exactly one positive literal is a definite clause or a strict Horn clause ; a definite clause with no negative literals is sometimes called a unit clause , and a unit clause without variables is sometimes called a fact ; and a Horn clause without a positive literal is sometimes called a goal clause ( note that the empty clause consisting of no literals is a goal clause ) .