def is_sorted(lst: list) -> bool:
    """
    Check if the list is sorted in ascending order.
    Use a loop to compare adjacent items. Equal neighbours are allowed.

    Parameters
    ----------
    lst : list
        The list to check. Its items must be comparable with <. Do not
        change the list.

    Returns
    -------
    bool
        True if the list is sorted, False otherwise. Empty and one-item
        lists are sorted.

    Examples
    --------
    >>> is_sorted([1, 2, 3])
    True
    >>> is_sorted([3, 2, 1])
    False
    >>> is_sorted([1, 2, 2, 3])
    True
    """
    raise NotImplementedError("Replace this line with your code.")