def keys_with_substring(dictionary, target, sensitivity = False):
    """
    Returns a list of keys from a dictionary that contain a target string,
    performing a case-insensitive comparison when sensitivity is False.

    Args:
        dictionary (dict): The dictionary to search within.
        target (str): The string to search for within the dictionary keys.
        sensitivity (bool): whether the checking is done in a case senstive way of a case insensitive way.

    Returns:
        list: A list of keys from the dictionary that contain the target string.
    """

    if sensitivity:
        return list(filter(lambda key: target in key, dictionary.keys()))
    else:
        return list(filter(lambda key: target.lower() in key.lower(), dictionary.keys()))