infix and prefix predicates/procedures
Most built-in constructs in Prolog, and, by default, the procedures and terms that you write yourself, use prefix syntax - that is, the name of the term/procedure (the functor) precedes the arguments (which are surrounded by parentheses and separated by commas). For example, when we use the built-in predicate member, we write something like member(Item, [a, b, c]) - first the predicate name, member, then "(", then the first argument, Item, then a comma, then the second argument, [a, b, c], then ")".

However, with built-in predicates like =, < and > that are usually written between their arguments, as in First < Max, we write, in Prolog as in mathematics, in infix notation. Another infix built-in "predicate" is is, which is used in evaluating arithmetic expressions.

It is possible in Prolog to define your own infix (and postfix) operators, and modify the syntactic handling of prefix operators - see op.