#pragma CIVL ACSL
$input int N;
$assume(0 < N);
int a[N];

int main() {

  int x = 0;
  /*@ loop invariant x == i;
    @ loop assigns a[0..N-1],x;
    @ focus F | a;
    @*/
  for (int i = 0; i < N; i++) {
    a[i] = i + x;
    x = x+1;
  }
  
  //@ focus F;
  $assert($forall(int i:0..N-1) a[i] == i+i);
}