The file lesson1.pl contains the clauses:

		has(jack,apples).
		has(ann,plums).
		has(dan,money).
		fruit(apples).
		fruit(plums).

		?- [lesson1]. 	/* loads the file */
		true.	
		?- listing(fruit). 	/* lists the clauses */
		fruit(apples). 
		fruit(plums). 			
		?- listing(has). 	
 		has(jack,apples). 
		has(ann,plums).
		has(dan,money).
		?- has(jack,X). 			/* what has Jack? */
		X = apples
		?- has(jack,_).  		/* does Jack have something? */
		true. 
		?- has(X,apples),has(Y,plums). /* who has apples and who has plums? */
		X = jack 
		Y = ann 
		?- has(X,apples),has(X,plums). /* does someone have apples and plums? */
		false. 
		?- has(dan,X),fruit(X). 	/* has Dan fruits? */
		no 
		?- has(X,Y),not(fruit(Y)). /* does someone have something else? */
   		X = dan
   		Y = money