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{
  package Base;

  sub new {
    my $class = shift;
    my $self = {}; # no parent
    bless $self, $class;
    print "new Base\n";
    return $self;
  };

  sub base_value {return 1;}
}


{
  package Derived;
  our @ISA = qw(Base);  # establishes inheritance

  sub new {
    my $class = shift;
    my $self = $class->SUPER::new(@_);  # relies on established inheritance
    print "new Derived\n";
    return $self;
  };

  sub derived_value {return 2;}
}


BEGIN {
  my $derived = Derived->new();
  my $b = $derived->base_value();
  my $d = $derived->derived_value();
  print "base_value = $d$b\n";
  print "derived_value = $d\n";
}

new Base
new Derived
derivedbase_value = 21
basederived_value = 1
2