#! perl -slw
use strict;
use Data::Dumper;

sub diffAoA{
	my( $p, $q ) = @_;
	( $p, $q ) = ( $q, $p ) if @$p < @$q;
	my %lookup = map{ join( '|', @$_ ), undef } @$p;
	delete @lookup{ map{ join( '|', @$_ ) } @$q };
	return map{ [ split '\|' ] } keys %lookup;
}

my @A0A1 = (
    [2003,1],[2003,3],[2003,4],[2004,1]
);

my @A0A2 = (
    [2003,1],[2003,2],[2003,3],[2003,4],[2003,5],[2003,6],
    [2003,7],[2003,8],[2003,9],[2003,10],[2003,11],[2003,12],
    [2004,1],[2004,2]
);

my @diff = diffAoA \@A0A1, \@A0A2;

print Dumper \@diff;

__END__
P:\test>test3
$VAR1 = [
          [ '2004',  '2' ],
          [ '2003', '12' ],
          [ '2003',  '5' ],
          [ '2003',  '2' ],
          [ '2003',  '9' ],
          [ '2003',  '8' ],
          [ '2003', '11' ],
          [ '2003',  '7' ],
          [ '2003', '10' ],
          [ '2003',  '6' ]
        ];