----------------------------------------------------------------------
free_vars                                                       (Term)
----------------------------------------------------------------------
free_vars : term -> term list

SYNOPSIS
Returns the set of free variables in a term.

KEYWORDS
variable, term.

DESCRIBE
An invocation {free_vars tm} returns a list representing the set of
term variables occurring in {tm}.

FAILURE
Never fails.

EXAMPLE

- free_vars (Term `x /\ y /\ y ==> x`);
> val it = [`y`, `x`] : term list




COMMENTS
Code should not depend on how elements are arranged in the
result of {free_vars}.

{free_vars} is not efficient for large terms with many free variables.
Demanding applications should be coded with {FVL}.



SEEALSO
Term.FVL, Term.free_vars_lr, Term.free_varsl, Term.empty_varset,
Type.type_vars.

----------------------------------------------------------------------