I'm learning probability and I've just found this on a book:
$$\sum_xP(x)=\sum_{x_1}···\sum_{x_n}P(x_1,...,x_n)=1$$
The bold $x$ is $x=(x_1,x_2,...,x_n)$.
My question is: How can I compute those $\sum_{x_1}...\sum_{x_n}$?
I think the expression means this (multiply each summation):
$$\sum_xP(x)=\sum_{x_1}P(x_1)·\sum_{x_2}P(x_1,x_2)·...·\sum_{x_n}P(x_1,x_2,...,x_n)$$
By the way, I'm trying to calculate the joint probability.