I'm reading the proof of the generating function but i'm not able to understand how did they change the multiplication of sums to one sum.
I would be grateful for help
Thanks
Nachum
generating-functions
I'm reading the proof of the generating function but i'm not able to understand how did they change the multiplication of sums to one sum.
I would be grateful for help
Thanks
Nachum
Best Answer
Just Cauchy's product followed by some cleanup.