assert(!equal([1, 2 ].s[], [1, 2, 3].s[]));
assert(!equal([1, 2, 3].s[], [1, 2, ].s[]));
assert( equal([1, 2, 3].s[], [1, 2, 3].s[]));
assert(!equal([1, 2 ].s, [1, 2, 3].s));
assert(!equal([1, 2, 3].s, [1, 2, ].s));
assert( equal([1, 2, 3].s, [1, 2, 3].s));
ditto