sub serialize {
    my @copy = @_;
    foreach my $o ( @copy ) {
        $o =~ s/\\/\\\\/g;  # escape escape char
        $o =~ s/,/\\,/g;    # escape delimiter
    }
    return join q{,}, @copy;
}

sub in_list {
    my ( $la_ref, $lb_ref ) = @_;

    my @la = @{$la_ref};
    my @lb = @{$lb_ref};

    return ( !@la || 0 <= index serialize( @lb ), serialize( @la ) );
}