Originally Posted by

**earthboy** My book says that it is readily seen that this definition can be written as a set of $\displaystyle 2^n$ equations, obtained from the last equation on replacing an arbitrary number of events $\displaystyle A_{j }$ by their complements $\displaystyle A'_{j}$, using the fact that if $\displaystyle A$ and $\displaystyle B$ are independent then $\displaystyle P(AB')=P(A)P(B')$ I cant understand what it means or how they arrive at $\displaystyle 2^n$ equations, or even how it gives 4 equations for 2 events, using the complements.