+ @# sed-fu: remove lines starting with "//@", and replace those ending in "/*@*/" by "unimplemented!()".
+ @# Also coalesce multiple adjacent such lines to one.
+ @sed '/^\s*\/\/@/d;s|\(\s*\)\S.*/\*@\*/|\1unimplemented!()|' $< | sed -f dup-unimpl.sed > $@