for my $x ( sortit() ) {  
    unless ( $seen{$x->[1]} ) { 
        print "$x->[0]\t$x->[1]\n"; 
        $seen{$x->[1]}++; 
    } 
    else { 
        print STDERR "Oh noes! Duplicate: $x->[0] $x->[1]\n"; 
        die; 
    } 
}