{
    my $i = 60000;
    my %h = (new => {});
    my $r = \%h;
    my $end = $r;   # end of the list
    for (0..$i) {
       print $_, " ";
       $r = $r->{new};
       $r->{new} = {};
       $r->{new}->{old} = $r;   # keep back-references
       $end = $r->{new};
    }
    print "end 1\n";
    while ($end) {  # delete the list from the end
        delete $end->{new};
        $end = delete $end->{old};
    }
}
print "end 2\n";