Past exam of the year 1 of the computer science course of the University of Oxford / 2014 / Discrete mathematics, continuous mathematics and probability / 1 / c / Solution

Apply the two identities already proved with $A=\mathcal{U}$. Every $B_i$ is a subset of the common universe, and a complement is the set difference from that universe. ThereforeReplacing each set difference from $\mathcal{U}$ by its complement notation gives the claimed finite forms of De Morgan's laws.