Working out a conjectured syntax for slicing long lists in a Perl 6 signature

median-of-three-conjecture.p6

multi quicksort([$head, *@front, $mid, *@back, $tail]) {
    my ($pivot, @others) := median-of-three($head, $mid, $tail);
    my @rest := |@others, |@front, |@back;

    quicksort(@rest.grep(* <  $pivot)),
    $pivot,
    quicksort(@rest.grep(* >= $pivot))
}
multi quicksort([$a, $b]) { $a < $b ?? $a, $b !! $b, $a }
multi quicksort(@a [$a?]) { @a }

my @x = 5, 8, 1, 9, -2, 3, 6;
say quicksort(@x).perl