-can also include hosted headers like <errno.h> that were present in
-Unix Version 7 and are thus widely available. Similarly, many modules
-include <sys/types.h> even though it's not even in C99; that's OK
-since <sys/types.h> has been around nearly forever. <string.h> and
+can also assume the existence of <ctime.h>, <errno.h>, <fcntl.h>,
+<locale.h>, <signal.h>, <stdio.h>, <stdlib.h>, <string.h>, and
+<time.h>. Some of these headers, such as <errno.h>, were present in
+Unix Version 7 and are thus widely available. <string.h> and