M9. Each package should use a limited and well-defined symbol, macro, library, and include file name space. For example, there should be no publicly visible include files such as utils.h, or package named libutil.a or macros name YES or TRUE. Namespacing of include files can be handled either by prepending each include file with a package name, for example <XXXmat.h>, or by placing and referencing all include files in a subdirectory with a package name, for example <XXX/mat.h>. Note that using a -I/XXX/ and referencing via <mat.h> would not be acceptable namespacing.