1.NounA Horn clause with exactly one positive literal."The clauses
¬
p
∨
q
{\displaystyle \neg p\vee q}
,
¬
p
∨
¬
q
∨
r
{\displaystyle \neg p\vee \neg q\vee r}
, and
¬
p
∨
¬
q
∨
¬
r
∨
s
{\displaystyle \neg p\vee \neg q\vee \neg r\vee s}
are examples of definite clauses. At least in classical logic these would be equivalent to the formulae
p
→
q
{\displaystyle p\rightarrow q}
,
(
p
∧
q
)
→
r
{\displaystyle (p\wedge q)\rightarrow r}
, and
(
p
∧
q
∧
r
)
→
s
{\displaystyle (p\wedge q\wedge r)\rightarrow s}
, respectively."