Thanks, Ollie - I'm happy with 9d now. However, with 20a the cell entries in positions 2, 4, 5, and 6 are fixed by thematic material. The 'a' in 20a cannot be in position 3 because of 9d and can't be in position 1 because of 8d. My answers to 20a, 8d, and now 9d seem beyond doubt, but there's clearly something wrong.