from typing import List


def _merge(indices1: List[int], indices2: List[int]) -> List[int]:
    """Merge the two list of the indices. Each list must be sorted.

    --------------------
    Args:
        'indices1': A sorted list of the indices.
        'indices2': A sorted list of the indices.

    --------------------
    Returns:
        The ordered list of indices.

    """
    merged_list = indices1 + indices2

    index1 = 0
    index2 = 0

    merge_index = 0

    while index1 < len(indices1) and index2 < len(indices2):
        if indices1[index1] < indices2[index2]:
            merged_list[merge_index] = indices1[index1]
            index1 += 1
        else:
            merged_list[merge_index] = indices2[index2]
            index2 += 1
        merge_index += 1

    for i in range(index1, len(indices1)):
        merged_list[merge_index] = indices1[i]
        merge_index += 1

    for i in range(index2, len(indices2)):
        merged_list[merge_index] = indices2[i]
        merge_index += 1

    return merged_list