De Morgan's Laws (Set Theory)/Set Complement/Complement of Union/Venn Diagram

Theorem

$\overline {T_1 \cup T_2} = \overline T_1 \cap \overline T_2$

Proof

Demonstration by Venn diagram:

$\overline T_1$ is depicted in yellow and $\overline T_2$ is depicted in red.

Their intersection, $\overline T_1 \cap \overline T_2$, is depicted in orange.

As can be seen by inspection, this also equals the complement of the union of $T_1$ and $T_2$.