sub c{f($_[0],$_[0]-$_[1]+1) / f($_[1],1)}
sub f{eval join'*',$_[1]..$_[0]}

##</code><code>##

sub c{f($_[0]-$_[1]+1..$_[0])/f(1..$_[1])}
sub f{eval join'*',@_}