void abort() { };
                                                                                                                                                          
                                                                            

/*@ 
    requires ((\old(n) <= 2));
    ensures ((\old(n) <= 2));
@*/
void f(int n) {
  if (n<3) return;
  n--;
  f(n);
  ERROR: {/*@ assert(0); */;abort();}
}

int main() {
  f(2);
}