The analogy to Harrods natural rate of
growth can be easily found in Hansen
when he assumes that the declining rate of
population and of technical progress
leads to maladjustment in relation to the saving structure.
( Actually Hansens way of thinking was here rather different
since the assumed ? growth to affect spending
whereas in Harrod this sets merely a ? to capacity growth!
Hansen also seems to consider more the effects of
of technical progress on the investment opportunities
-i.e. on I rather than on the 
? productivity and thus natural rate of growth).

My own views on maturity
My own views on maturity