Solution
= Solution
\b[False.] Take the <sets> $A=\{1\}$, $B=\varnothing$ and $C=\{1\}$. Both <unions> with $C$ equal $\{1\}$, although $A\ne B$. Taking a <union> with $C$ conceals which of its elements belonged to the original <set>.
= Solution
\b[False.] Take the <sets> $A=\{1\}$, $B=\varnothing$ and $C=\{1\}$. Both <unions> with $C$ equal $\{1\}$, although $A\ne B$. Taking a <union> with $C$ conceals which of its elements belonged to the original <set>.