David's A5 Wagyu

David is firing up the barbecue to sear a thick cut of A5 Wagyu. Because David treats steak as an exact science, he demands a mathematically perfect 45° crosshatch sear over a BMS 12 marbling pattern.

Print the 19×9 ASCII representation of David's steak (x from 0 to 18 horizontally, y from 0 to 8 vertically) using the following priority rules for each coordinate (x, y):

1. Corners: Print / at (0, 0) and (18, 8). Print \ at (18, 0) and (0, 8).
2. Crust: Print # along the remaining outer border (x == 0, x == 18, y == 0, or y == 8).
3. Grill Marks: Inside the border, let a = (x + y) % 4 == 0 and b = (x - y) % 4 == 0.
   • If both a and b are true, print X.
   • If only a is true, print /.
   • If only b is true, print \.
4. Intramuscular Fat (A5 Marbling): Otherwise, if (x * y) % 3 == 0, print ..
5. Prime Beef: For all remaining cells, print @.