-- |The length of a series with n elements, is at most n elements.
-- (It can be less due to the series never generating new elements, 
-- such as 0.0 0.0 2.)
prop_lengthOfSeriesN :: Double -> Double -> Int -> Property
prop_lengthOfSeriesN fstNum growthRate len = len >= 0
                                               ==> (length (seriesN fstNum growthRate len) <= len)
prop_lengthOfSeriesN :: Double -> Double -> Int -> Property
prop_lengthOfSeriesN fstNum growthRate len = len >= 0
                                               ==> (length (seriesN fstNum growthRate len) <= len)
prop_lengthOfSeriesN fstNum growthRate len = len >= 0
                                               ==> (length (seriesN fstNum growthRate len) <= len)