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FVL                                                             (Term)
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FVL : term list -> term set -> term set

SYNOPSIS
Efficient computation of the set of free variables in a list of terms.

KEYWORDS
variable, free, set.

DESCRIBE
An invocation {FVL [t1,...,tn] V} adds the set of free variables found
in {t1,...,tn} to the accumulator {V}.

FAILURE
Never fails.

EXAMPLE

- FVL [Term `v1 /\ v2 ==> v2 \/ v3`] empty_varset;
> val it = <set> : term set

- HOLset.listItems it;
> val it = [`v1`, `v2`, `v3`] : term list




COMMENTS
Preferable to {free_varsl} when the number of free variables
becomes large.

SEEALSO
HOLset, Term.empty_varset, Term.free_varsl, Term.free_vars.

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