It's all in the 2's follow-up question

Question

This is in regards to the solution in Slitherlink - It's all in the 2s

I know it may seem dumb, but I don't understand the logic behind the second 2 chain in the solution. To help provide clarity in my question, imagine that each dot corresponds to a Letter-Number coordinates like

7 
6 
5 
4 
3 
2 
1 
  ABCDEFG

The line the is next to the top 2 in the diagonal pair where the line goes from G-4 to G-5.

I'm also lost on why there is a line from G-2 to G-3?

Thanks in advance for teaching me.

Answer 1

Good question, the chain is not immediately obvious but I think this is the line of reasoning

The highlighted node in the picture cannot provide an entry or exit from the 2 square for the path

This means that the two adjacent nodes are the entry/exit points (the path either uses the top and left sides or bottom and right). The knock-on effect is that the highlighted node below is also not an entry/exit node for its square

and similarly the two adjacent nodes (to the right and below) are entry/exit for that 2 square (below-right of the highlighted node). In particular, the following node is an entry exit point

as must be the node above and to the right and the exiting path can only be continued upwards from there (i.e, G-4 to G-5)

The G2-G3 line only comes after filling in a few lines first

And then we see the chain