def cond_sum(a, b, lb=10, ub=19):
    """
    Returns the sum of a and b given that it is in [lb, ub]
    
    lb : lower bound (included) of the interval when it returns 20
    ub : upper bound (included) of the interval when it returns 20

    """
    summ = a + b
    if summ >= lb and summ <= ub:
        return 20
    else:
        return summ