Analyzing and Constructing Terms

The built-in predicate functor/3 performs these functions

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

The built-in predicate arg/3 performs these functions:

• Unifies a term with a specified argument of another term.

The built-in predicate Term =.. List performs these functions:

• The built-in predicate =../2 (otherwise known as "univ") 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.