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Exercise 2.1
Exercise 1: Prove that the empty set is a subset of every set.
Answers
Let be any set. The empty set is a subset of iff for all , . This is vacuously true, so we are done.
Comments
Proof. To prove for all sets , we have to prove that every element is also in by Definition 1.3. Since there are no points in by Definition 1.3, is a subset of every set. □