PROLOG program:

write_descendant_chain. Later chapters examine the special predicates write and nl, which can be used to produce output other than just the values of variables.

For example, if there is a clause

write_child(X,Y) :- write(X), write( is a child of ), write(Y), nl.

then the query write_child(john_smith,sue_jones) will always succeed and will also print john_smith is a child of sue_jones on one line. Include this predicate in your program, and write the clauses for a predicate write_descendant_chain(x,y) that prints a chain from x to y when x is a descendant of y but prints nothing when x is not a descendant of y.

For example, if John Smith is a descendant of William Brown, then write_descendant_chain(john_smith,william_brown) should print a sequence of lines something like this: john_smith is a child of sue_jones

sue_jones is a child of harvey_jones

harvey_jones is a child of davy_jones

davy_jones is a child of anna_brown

anna_brown is a child of william_brown

Hint: You will not be able to use the descendant predicate you de?ned for this. Use the child predicate together with write_child. Also, work down from y rather than up from x.

I do have query of child(X,Y), ancestor(X,Y), desendant(X,Y)... and KB.