@staticmethod
def is_functional_var(var_name):
    """
        Assumes var_name is a legal variable name (doesn't check). Returns
        True iff var_name is a functional variable name

        Parameters
        ----------
        var_name : str

        Returns
        -------
        bool

        """
    assert isinstance(var_name, str) and len(var_name) >= 2
    if var_name[0] == '-':
        if not var_name[1].islower():
            return False
    elif not var_name[0].islower():
        return False
    return True
