Louden, Figure 7.5.

int x = 2;

void g(int);

void f(int n) {
  static int x = 1;
  g(n);
  x--;
}

void g(int m) {
  int y = m-1;
  if (y<0) {
    f(y);
    x--;
    g(y);
  }
}

int main(void) {
  g(x);
  return 0;
}