Functions

• We can also have functions like tall(x).
• If x is a constant, this returns true or false.
• If it's a variable, it returns a set (perhaps empty) of all the constants that are true for this function.
• Note that returning here really depends on the implementation. In many prologs, the set is returned to the interpretter.
• This gives us a lot of power, because now we've moved to a potentially infinite number of statements.