In formal logic, Horn-satisfiability, or HORNSAT, is the problem of deciding whether a given conjunction of propositional Horn clauses is satisfiable or not.
[2] The extension of the problem for quantified Horn formulae can be also solved in polynomial time.
[3] The Horn satisfiability problem can also be asked for propositional many-valued logics.
Simplification gives Now it is a trivial case, so the remaining variables can all be set to false.
Thus, a satisfying assignment is In the Horn formula one clause forces f to be true.