Meaning of constant $\{N_{i}\}$

Question

I have a doubt concerning the notation $\{N_{i}\}$. In in the derivation at constant $\{N_{i}\}$ of a number (like $\left(\frac{dA}{dB}\right)_{\{N_{i}\}}$) does this notation mean that the total number of the ensemble is kept constant, or that the number of of each individual N ($N_{1}$, $N_{2}$, $N_{3}$... ) is kept constant.

I am assuming it is the later, but I can't convince myself.

Thanks.

Answer 1

As it turns out I found the answer while looking for an example for Paul Sinclair. It does mean each specie is at constant number. Sorry if the question is unclear and thank you.