https://svn.boost.org/svn/boost/trunk ........ r54067 | eric_niebler | 2009-06-18 14:39:09 -0700 (Thu, 18 Jun 2009) | 1 line add a sensible default for proto::_default's template parameter ........ [SVN r54068]
https://svn.boost.org/svn/boost/trunk [SVN r53591]