CDO2 — 4.2

The flavour text hints at the Coordinates module.

The first entry, 81, suggests that we are dealing with a grid size of 9×9. The grid we constructed earlier in the CDO puzzle has those dimensions.

The remaining entries are coordinates pointing at locations in that grid. When we convert these coordinates in column order, we find that some of them are duplicates:

2,3 C2 #3 C9
6,1 A6 #18 I8
9,5 E9 #54 I4
7,4 D7 #81 I1
B2 B2 5th E1
F8 F8 10th A2
H4 H4 30th C4
I9 I9 46th A6 R
<1,1>B2 A 1/3 C9 E
<5,5>F6 6/2 B4
<8,0>A9 9/5 E1 S
<8,4>E9 R 2/9 I8 T

In the order in which the coordinates become duplicates, they spell out the solution.