(\bigcap_{n=1}^{\infty}E_n)^c=\bigcap_{n=1}^{\infty}E_n^c=\bigcap_{i=n}^{\infty}(\bigcup_{i=1}^{\infty}D_i)^c=\bigcap_{i=n}^{\infty}(\bigcap_{n=1}^{\infty}D_i^c)=\bigcap_{n=1}^{\infty}D_n^c