Let's rewrite that slightly differently and just say l over L  open brackets into D T P L over D L  minus T P over L , alright, what's that in economic terms, well that's simply , right, marginal product of labour in the brackets, right, minus the average product of labour , okay, so if  if the marginal product of labour here is greater than the average product  right, the righthand side is going to be positive  right, therefore, average product is going to be positive  okay,the marginal product is greater than the average product ah change  the slope of the average product curve is going to be er positive therefore average product itself is positive and rising  let's write that down as the marginal product of labour is greater than the average product of labour  that implies  changing slope of the er  average product curve right, is positive  implying that average product is positive itself and rising  Okay, if the marginal product of labour, right, is less than the average product  right, that implies   the slope of the average product curve is positive therefore the average product itself, right, is positive and falling   sorry    right, so we can rewrite that somewhat succinctly , using the following   D A P L over D L, right, is greater than equal to or less than zero  if  D T P L over D L, right, is greater than, equal to, less than  right T P L over L the average product .