Backpropagation chain rule example My question is in regards to an MIT course example.



The instructor delves into the backpropagation of this simple NN. 



I have two questions. 


Why do we seem to disregard the weights of the second layer (in blue)? 
The red circle, should this not be $\partial y_2$ (followed by $\frac{\partial y_2}{\partial P_3}$)?
Why do we seem to disregard the weights of the second layer (in blue)?
-----because activation function is after that block, so differential with the o/p y is as good as with the weight.
The red circle, should this not be ∂y2 (followed by ∂y2∂P3)?
-----y2 and y1 is the o/p of the same block i.e. both must be same