text: extern void abort(void); 
  void reach_error(){}
  
  int sum(int n, int m) {
      if (n <= 0) {
        return m + n;
      } else {
        return sum(n - 1, m + 1);
      }
  }
  
  int main(void) {
    int a = 2;
    int b = 3;
    int result = sum(a, b);
    if (result != a + b) {
      ERROR: {reach_error();abort();}
    }
  }
  