The Real Number System

12345678
Across
  1. 1. 2
  2. 3. 3
  3. 7. is a...
  4. 8. 6
Down
  1. 2. 5
  2. 3. 9
  3. 4. of two...
  4. 5. Any...
  5. 6. 9
  6. 7. by a...