\DOC intersect

\TYPE {intersect : ''a list -> ''a list -> ''a list}

\SYNOPSIS
Computes the intersection of two `sets'.

\KEYWORDS
list, set, eqtype.

\DESCRIBE
{intersect l1 l2} returns a list consisting of those elements of {l1} that
also appear in {l2}.

\FAILURE
Never fails.

\EXAMPLE
{
- intersect [1,2,3] [3,5,4,1];
> val it = [1, 3] : int list
}


\COMMENTS
Do not make the assumption that the order of items in the list
returned by {intersect} is fixed. Later implementations may use
different algorithms, and return a different concrete result
while still meeting the specification.

A high-performance implementation of finite sets may be found in
structure {HOLset}.

ML equality types are used in the implementation of {intersect}
and its kin. This limits its applicability to types that
allow equality. For other types, typically abstract ones,
use the `op_' variants.

\SEEALSO
Lib.op_intersect, Lib.union, Lib.U, Lib.mk_set, Lib.mem, Lib.insert, Lib.set_eq, Lib.set_diff.
\ENDDOC