This header file simply cross-includes the header file oskit/exec/a.out.h, which is part of the executable interpreter library (see Section 23.1.2) and provides a minimal set of definitions describing a.out-format executable and object files. Although this header file is not standard ANSI or POSIX (thank goodness!), it is a fairly strong Unix tradition, and is especially relevant to operating system code, and therefore is provided as part of the OSKit.