> the rate (y) of increase of inflation (x) was decreasing (z). I guess first, does he mean that y, the rate at which x increases is going down by z? or that y

> the rate (y) of increase of inflation (x) was decreasing (z). I guess first, does he mean that y, the rate at which x increases is going down by z? or that y is down, but z is not its rate? And second, if you see inflation here as a derivative or not.