Warning: CHC: Out of bounds access happens here.
Counterexample:
arr = []
a = 0x0
x = 0

Transaction trace:
test.constructor()
State: arr = []
test.f(0x0, 1)
  --> model_checker_targets_out_of_bounds_chc/input.sol:13:3:
   |
13 | 		arr[x];
   | 		^^^^^^
