So, that is equal to delta of n minus m which means the double summation will collapse to a single summation will work with a single summation; summation over n I am going to take the expected value inside it will now be alpha n of t alpha n of t plus tau alpha n t plus delta t. So, that is one of the terms then notice that where ever this n and m are the same.
जिसका मतलब है कि डबल समेशन एक एकल योग के रूप में मिल जाएगा।