Set theory

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Across
  1. 4. a collection of elements.
  2. 5. #A
  3. 7. (a,b)
  4. 9. A ∩ B
  5. 10. |
  6. 11. both sets have the same members.
  7. 14. A - B
  8. 15. A ⊆ B
Down
  1. 1. A×B
  2. 2. A ∆ B
  3. 3. Ø = { }.
  4. 6. A \ B
  5. 8. all subsets of A.
  6. 12. meaning or definition of a∈A.
  7. 13. A ∪ B