sub Diff {
    my @a;
    my $dif = undef();
    for my $fdx (0..1) {
        open my $fh, $_[$fdx] or die "$!: $_[$fdx]\n";
        my @tmp = <$fh>;
        $a[0] = \@tmp;
        close $fh;
    }
    while ( $a[0] -> [0] and $a[1] -> [0] ) {
        if ( $a[0] -> [0] eq $a[1] -> [0] ) {
            shift @$a[0]; shift @$a[1];
        }
        elsif ( $a[0] -> [0] ) {
            $dif .= '< ' . shift( @$a[0] );  
        }
        else {
            $dif .= '> ' . shift( @$a[1] );
        }
    }
    return $dif;
}
##</code><code>##

sub Diff {
    my @a;
    my $dif = undef();
    my $found;
    for my $fdx (0..1) {
        open my $fh, $_[$fdx] or die "$!: $_[$fdx]\n";
        my @tmp = <$fh>;
        $a[0] = \@tmp;
        close $fh;
    }
    while ( $a[0] -> [0] and $a[1] -> [0] ) {
        if ( $a[0] -> [0] eq $a[1] -> [0] ) {
            shift @$a[0]; shift @$a[1];
        }
        elsif ( $found = Search( @a )) {
            $found--;
            for my $idx ( 0..$found ) {
                $dif .= '> ' . shift( @$a[1] );
            }
        }
        elsif ( $a[0] -> [0] and not Search( @a ) {
            $dif .= '< ' . shift( @$a[0] );  
        }
        else {
            $dif .= '> ' . shift( @$a[1] );
        }
    }
    return $dif;
}
sub Search {
    my $found = 0;
    my $max = $#$_[1];
    while ( $_[0] -> [0] ne $_[1] -> [$found] ) {
        $found++;
        ( $found >= $max ) and return 0;
    }
    return $found;
}