typedef struct 
  vac { 
  } vac;

typedef struct 
  biz { 
    int x; 
    void y; 
    int z;
  } biz;

int main(void)
  { biz A, B;
    A.y = B.y;
    void v;
    A.y = v;
    v = B.y;
    vac U, V;
    U = V;
    return 0;
  }