
Summary of Chapter 4 (OPERATORS)A binary predicate (any user-defined with two arguments) can be converted to an infix operator. This enables the functor (predicate name) to be written between the two arguments with no parentheses, e.g.likes (john, mary)...
http://discreteaddict.blogspot.com/2009/11/summary-of-chapter-4-operator-and_17.html