Wally and his friends are hiding on this page, can you find them?

Describe the image above with left_of(X,Y) that unifies if X is left of Y (not necessarily on the same line). You should base your implementation on is_left_of/2 and is_below_of/2.

is_left_of(waldo,odlaw).
is_left_of(odlaw,swi).
is_left_of(swi,wilma).
is_left_of(whitebeard,woof).
is_left_of(woof,watchers).

is_below_of(whitebeard,waldo).
is_below_of(woof,odlaw).
is_below_of(watchers,swi).

You can download the facts above as database.pl¹