def translate_simple_correlation(corr_string: str) -> dict:
    """
    Translates a string describing a correlation definition with standard correlation
    variables (x, y, z, t) in a dictionary that can be used for correlation_info.

    Parameters
    ----------
    corr_string
        A string like 'T1:xy'. This string contains 3 elements. 'T1' can be any other
        string without a colon ':'. Afterwards, there must follow a colon ':'. Then, the
        last element is a number of non-repeating characters from ('x', 'y', 'z', 't').

    Returns
    -------
    corr_dict
        In the example, 'T1:xy' would be translated to {'T1': {'x': 'x', 'y': 'y'}}.
        This dictionary can be used for the 'correlation_info' argument when adding new
        experiments to an InferenceProblem.
    """
    if not (":" in corr_string):
        raise ValueError(f"The given 'corr_string' ('{corr_string}') contains no ':'!")
    sensors = corr_string.split(":")
    if len(sensors) > 2:
        raise ValueError(
            f"The given 'corr_string' ('{corr_string}') contains more than one ':'!"
        )
    corr_dict = {sensors[0]: {}}  # type: dict
    for character in sensors[1]:
        if character not in ["x", "y", "z", "t"]:
            raise ValueError(
                f"The given 'corr_string' ('{corr_string}') does contain a non-standard"
                f" variable ('{character}' instead of 'x', 'y', 'z', 't') after the "
                f"colon ':'!"
            )
        corr_dict[sensors[0]][character] = character
    return corr_dict