Composite or Prime?

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Across
  1. 4. Choir sang 25 pages (5)
  2. 7. Ship giant one office (7)
  3. 8. Long speech for broad cast trawl? (5)
  4. 10. Deranged police pact filled with rage (10)
  5. 11. Stars aligned for three years in Salzburg (6)
  6. 13. Headless Duck or Beaver results in a tie (5)
  7. 15. Experimental sci-fi stuff leads to fist fights (10)
  8. 17. Average stroke direction (8)
  9. 18. Weapon for Cuban revolutionary inmate (7)
Down
  1. 1. Mum bled iron resilience (6)
  2. 2. Arcane abide fanatically by alphabetical order (11)
  3. 3. A fresh peach on sale (5)
  4. 5. Confident detective has new Tinder profile? (8)
  5. 6. Insipid dictator breakfast staples (11)
  6. 9. Removing the cash register for treat? (7)
  7. 12. Complaint during yak vet check-up (6)
  8. 14. Out re: office--creating hairstyle (6)
  9. 16. Figured fabric: satin solaces (4)