4.8.2 Analyzing and Constructing Terms

The built-in predicate functor/3:

• decomposes a given term into its name and arity, or
• given a name and arity, constructs the corresponding compound term creating new uninstantiated variables for its arguments.

The built-in predicate arg/3 unifies a term with a specified argument of another term.

The built-in predicate Term =.. List unifies List with a list whose head is the atom corresponding to the principal functor of Term and whose tail is a list of the arguments of Term.