I have a fact:
loves(romeo, juliet).
then i have an 'or' rule:
dances(juliet) :- loves(romeo, juliet).
dances(juliet) :- dancer(juliet).
As you can see dancer fact does not exist but this should be no problem and dances(juliet) should return me true. Instead it returns me true and then throws an exsitence exception about dancer fact. Is there a way to write rules for non existent facts or rules? Do I need to check if the fact exists?