Two of the predominant types of relationships in knowledge-representation systems are predication and the universally quantified conditional.

It is based on the idea that each validation is encapsulated by a simple, stateless predicate that receives some input and returns either true or false.

the function you pass to the find method is called a predicate. The predicate here defines a boolean outcome based on conditions defined in the function itself, so that the find method can determine which value to find.