-//pid_t wait3 (int *, int, struct rusage *);
-//pid_t wait4 (pid_t, int *, int, struct rusage *);
+
+#ifdef _GNU_SOURCE
+#include <sys/resource.h>
+pid_t wait3 (int *, int, struct rusage *);
+pid_t wait4 (pid_t, int *, int, struct rusage *);
+#endif