 
 
 
| capital(london, england). brother(fred, jane). | 
Head :- Body.where Head is a structure (or atom) and Body is a Goal, possibly with conjunctions and disjunctions like in the queries discussed above. The following is a clause
| uncle(X,Z) :- brother(X,Y), parent(Y,Z). | 
uncle(X,Z) ←— brother(X,Y) ∧ parent(Y,Z)or, more precisely
∀ X ∀ Z: uncle(X,Z) ←— ∃ Y: brother(X,Y) ∧ parent(Y,Z)stating that uncle(X,Z) is true if brother(X,Y) and parent(Y,Z) are true. Note that a fact is equivalent to a clause where the body is true:
| brother(fred, jane) :- true. | 
| parent(abe, homer). parent(abe, herbert). parent(homer, bart). parent(marge, bart). | 
| ancestor(X,Y) :- parent(X,Y). ancestor(X,Y) :- parent(Z,Y), ancestor(X,Z). | 
 
 
