// verifast_options{disable_overflow_check target:ILP32}

extern void abort(void);//@ requires true; 
//@ ensures true;

extern void __assert_fail(const char *, const char *, unsigned int, const char *) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__noreturn__));
void reach_error() //@ requires false; 
//@ ensures true;
{ __assert_fail("0", "sum_20x0-2.c", 3, "reach_error"); }

int sum(int n, int m) //@ requires true; 
//@ ensures (result == (n + m));
{
    if (n <= 0) {
      return m + n;
    } else {
      return sum(n - 1, m + 1);
    }
}

int main(void) //@ requires module(sum_20x0_2__verifast_instrumented_modified, true); 
//@ ensures junk();
{
  int a = 20;
  int b = 0;
  int result = sum(a, b);
  if (result != a + b) {
    ERROR: {reach_error();abort();}
  }
}