I think bounded and un-bounded are equivalent and that the same rules apply. You can often transform a bounded variable to an unbounded one and visa versa. For instance, for a moving average you can look at the period from 1 to infinity. If you in stead look at frequency (which is equivalent) you're looking at the range of 1 to 1/infi=0, i.e. the bounded interval of ]0;1]. Both are valid and mean the same.