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+See: https://adventofcode.com/2020/day/1
+** Part 1
+*** Purpose
+Given a list of numbers (report):
+
+#+begin_example
+1721
+979
+366
+299
+675
+1456
+#+end_example
+
+This program takes two entries that sum to 2020 (in the above example, it is 1721 and 299) and multiplies them together.
+
+*** Method
+
+To do this, the program takes the full list of numbers and subtracts them from 2020:
+
+#+begin_example
+299
+1041
+1654
+1721
+1345
+564
+#+end_example
+
+It stores this as a list of cons pairs:
+
+#+begin_example
+'((299 . 1721)
+ (1041 . 979)
+ (1654 . 366)
+ (1721 . 299)
+ (1345 . 675)
+ (564 . 1456))
+#+end_example
+
+Now, we find a pair that is equivalent on the basis of containing the same elements, and complete the multiplication.
+
+** Part 2
+*** Purpose
+Of course, we now need to find three numbers in the list that meet the same criteria...
+
+Say we have a list:
+
+#+begin_example
+979
+366
+675
+#+end_example
+
+We calculate a list of key-value pairs---each number added to every other number...
+
+#+begin_example
+'((((979 366) . 1345)
+   ((979 675) . 1654)
+   ((366 675) . 1041))
+#+end_example
+
+Then, we perform the same operation as we did in the first part:
+
+#+begin_example
+'((((979 366 675) . 1345)
+   ((979 675 366) . 1654)
+   ((366 675 979) . 1041)))
+#+end_example
+
+And we simply check if all three values in the car position are in the original set of numbers.