It may sound ridiculous but I can't find this anywhere on the web.
Thanks in advance
I dont know how to answer. I have two exercisses from a book both say to define the NOT version of the Inclusion-Exclusion principle for three subsest A1,A2,A3 of a set A.The second exercise wants a formula for for the number of elements in A that don't belong in A1,A2,A3,A4.And I can't find it
Say that $\displaystyle \mathcal{U}$ is a finite set and $\displaystyle A_k\subseteq\mathcal{U}$ for $\displaystyle k=1,2,3,4$.
Then $\displaystyle \|\mathcal{U}\|-\|\overline{A_1}\cap\overline{A_2}\cap\overline{A_ 3}\cap\overline{A_4}\|$ is the number of elements NOT in $\displaystyle A_1\cup A_2\cup A_3\cup A_4$
That is a guess as to what it may mean.