<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def add_accent_char(char, accent):
 """ Add accent to a single char. Parameter accent is member of class Accent """

    if char == "":
        return ""
    case = char.isupper()
    char = char.lower()
    index = utils.VOWELS.find(char)
    if (index != -1):
        index = index - index % 6 + 5
        char = utils.VOWELS[index - accent]
    return utils.change_case(char, case)