+/* Map region identifier. */
+typedef int mapid_t;
+#define MAP_FAILED ((mapid_t) -1)
+
+/* Maximum characters in a filename written by readdir(). */
+#define READDIR_MAX_LEN 14
+
+/* Typical return values from main() and arguments to exit(). */
+#define EXIT_SUCCESS 0 /* Successful execution. */
+#define EXIT_FAILURE 1 /* Unsuccessful execution. */
+
+/* Projects 2 and later. */