Logic Symbols

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Across
  1. 2. what is this symbol &
  2. 3. what is this symbol ∄
  3. 7. what is this symbol |
  4. 12. what is this symbol !
  5. 14. what is this symbol '
  6. 15. what is this symbol ∀
Down
  1. 1. what is this symbol ¬
  2. 4. what is this symbol ≡
  3. 5. what is this symbol ⇒
  4. 6. what is this symbol ∣
  5. 8. what is this symbol ∴
  6. 9. what is this symbol ∃
  7. 10. what is this symbol ∵
  8. 11. what is this symbol ¬
  9. 13. what is this symbol +