# Compound Syntax

The simplest form of structuring terms is the compound. The compound consists of a name followed by one or many arguments. The principal name is called the functor and the number of arguments is called the arity. To disambiguate from operator expressions a compound is only recognized when the name directly precedes the left parenthesis (“(”).

`compound   --> "{" term(1200) "}"             | atom "(" arguments ")"             | atom "(" ")".arguments  --> term(999) { "," term(999) }. `

Examples:
`f(a,b)         % is a compound{}             % is the empty set, corresponds to '{}'{a}            % is a compound, corresponds to '{}'(a)-(a,b)         % is a compound, corresponds to a - b- (a, b)       % is an expression, corresponds to - ,(a, b)`

By means of the braces (“{}”) a form of set notation can be invoked. The empty set notation is just a short hand for the name ‘{}’. The set notation that surrounds a term is a compound of arity one with the functor ‘{}’. Since the empty set {} and the empty list [] do belong to the category of atoms they can be used as a functor as well.