@staticmethod
def explain(formula):
    """
        разбить на части
        """
    level = 0
    formula1, formula2 = '', ''
    sub_formules = 1
    for alfa in formula:
        if alfa == '[':
            level += 1
        if alfa == ']':
            level -= 1
        if alfa == '~' and not level:
            sub_formules += 1
        elif sub_formules == 1:
            formula1 += alfa
        elif sub_formules == 2:
            formula2 += alfa
    return [formula1, formula2]
