Interjecting. Talking of conventions, it is likely that Boost picked it up from the C++ iostream (heavy) and iosfwd (light) standard headers. Chetan From: [email protected] [mailto:[email protected]] On Behalf Of Jed Brown Sent: Friday, February 15, 2013 2:51 PM To: For users of the development version of PETSc Subject: Re: [petsc-dev] Forward declarations of types? On Fri, Feb 15, 2013 at 4:39 PM, Jed Brown <[email protected]> wrote: petsc*fwd.h or petsc*types.h? Is there an established convention here? Here's one documented convention. http://lists.boost.org/Archives/boost/2001/07/14827.php