def get_concat_level_bits(n, adder):
  """Create a string of concat ops for the bits of the sum at the given adder.

  Args:
    n: An integer, the number of bits to concatenate
    adder: An integer, represents the index of the add that we're at in the
      chain.

  Returns:
    The chain of concats.
  """
  concats = [f"s_{adder}_0"]
  for i in range(1, n):
    rhs = concats[i - 1]
    concat = ["(concat", f"s_{adder}_{i}", rhs + ")"]
    concats.append(" ".join(concat))
  return concats[-1]