Prolog Tutorial - Facts with Arguments Facts with Arguments More complicated facts consist of a relation and the items that this refers to. These items are called arguments.
Facts can have arbitrary number of arguments from zero upwards.
The above fact says that a relationship likes links john and mary. This fact may be read as either john likes mary or mary likes john. This reversibility can be very useful to the programmer, however it can also lead to some pitfalls. Thus you should always be clear and consistent how you intend to interpret the relation and when. Finally, remember names of the relations are defined by you.