import re


def check_edge_cases(expression):
    """checks for edge cases.

    Parameters
    ----------
    :param str expression: the expression to check.
    :return: True if all edge cases passes, otherwise return False.
    """
    # nothing to evaluate.
    if expression is None:
        return False

    # expression does not contain at least 2 digits.
    if len([x for x in expression if x.isdigit()]) < 2:
        return False

    # expression contains a letter.
    if re.compile('[a-zA-Z]+').search(expression) is not None:
        return False

    return True