#
# This software is Copyright 2005 by Elsevier Inc.  You may use it
# under the terms of the license at http://perl.plover.com/hop/LICENSE.txt .
#



###
### binary
###

## Chapter 1 section 1

sub binary {
  my ($n) = @_;
  return $n if $n == 0 || $n == 1; 
  my $k = int($n/2);
  my $b = $n % 2;
  my $E = binary($k);
  return $E . $b;
}