* len 2? digit is 1
* len 3? digit is 7
* len 4? digit is 4
* len 5?
  * is a superset of the code for 1? digit is 3
  * has a set difference of size 2 with the code for 4? digit is 2
  * else digit is 5
* len 6?
  * is a superset of the code for 4? digit is 9
  * else, is a superset of the code for 1? digit is 0
  * else digit is 6
* len 7? digit is 8

* output codes' digital values can be found via lookup using previous section's data
* an output code quartet is the string value of each output code on a line's corresponding digit, string-concatenated
* the sum is the set of all output code quartets, integer-added