{               # make $a and $b point to each other
    my($a, $b);
    $a = \$b;
    $b = \$a;
}
*****
{               # make $a point to itself
    my $a;
    $a = \$a;
}
*****
sub new_node {
    my $self = shift;
    my $class = ref($self) || $self;
    my $node = {};
    $node->{LEFT} = $node->{RIGHT} = $node;
    $node->{DATA} = [ @_ ];
    return bless $node, $class;
}
*****
#!/usr/bin/perl
package Subtle;

sub new {
    my $test;
    $test = \$test;   # Create a self-reference.
    warn "CREATING " . \$test;
    return bless \$test;
}

sub DESTROY {
    my $self = shift;
    warn "DESTROYING $self";
}

package main;

warn "starting program";
{
    my $a = Subtle->new;
    my $b = Subtle->new;
    $$a = 0;           # Break this self-reference, but not the other.
    warn "leaving block";
}

warn "just exited block";
warn "time to die...";
exit;