Zero Element of Union and Intersection
- Introduction to Set Theory
- $1$. Elementary Operations on Sets
This mistake can be seen in the 2009 Dover edition: ISBN 0-486-47222-1
- "The operations $A \cup B$ and $A \cap B$ are meaningful for every pair of sets $A, B$ ... The empty set $\varnothing$ plays the role of the zero element."
This is technically incorrect.