geom. declining ma

Hi, I would be very grateful if someone could help me with a problem. Im replicating a study with new panel data and must now proxy a variable by a given equation (from the study): π_(L,t) =(1-δ)*π_(L,t-1)+ δ*π_(t-1) :underscore means subscript It says that π_(L,t) is found from a weight on...