1: extern void a_function (void);
    2: extern void b_function (void);
    3: extern void c_function (void);
    4: extern void d_function (void);
    5: 
    6: void
    7: d_function (void)
    8: {
    9:   a_function ();
   10:   b_function ();
   11:   c_function ();
   12: }