#
# 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 .
#



###
### factorial
###

## Chapter 1 section 2

sub factorial {
  my ($n) = @_;
  return 1 if $n == 0;
  return factorial($n-1) * $n;
}