In quest 2, Zach won all 3 rules competitions. Let’s first look at part 1. In this gif, I’ve actually added a rule and changed 2 others to keep everything nice and horizontal. Originally the @’s went up and down.

Features:

1. There are 5 heads. 1 to read the string, 2 to write @’s for A pairs and 2 to write @’s for B pairs.
2. When there’s an A in the string, an @ is written above the string and an @ might be deleted below the string. If there are 2 A’s in a row, the written @ for the 1st A is left alone. And vice versa.

Part 2 is similar. There’s an extra rule to go back to the beginning of a line.

For part 3, again there are new features. Going down and up a column are very different. There are different mechanisms for the horizontal and vertical pairs.

Truth be told, I haven’t quite wrapped my head around part 2 and 3 here. But I see the general features.

Code .