# Thread: Inclusion - Exclusion Principle

1. ## Inclusion - Exclusion Principle

Let S = {n1*a1, n2*a2, ..., nk*ak}, and let r be a natural number such that there is at
least one r-combination of S. Show that in applying the inclusion-exclusion principle to determine the number of r-combinations of S, one has A1 n A2 n ... n Ak = EmptySet.

n = intersection

Thanks in advance for any help on this one...

2. Originally Posted by jzellt
Let S = {n1*a1, n2*a2, ..., nk*ak}, and let r be a natural number such that there is at least one r-combination of S. Show that in applying the inclusion-exclusion principle to determine the number of r-combinations of S, one has A1 n A2 n ... n Ak = EmptySet.
I have absolutely no idea what any of that means.
That notation is completely "off the wall".