#A65: Tetrochain (CTB, Y, and K)

 I remember Tetrochain-Y as the O.G. Tetrochain. It's cool that this genre has the distinction of having other official genres with the same shading constraints under different clue types, instead of just as special variants of one puzzle. If I had to guess, CTB likely stands for "Cross The Borders", Y for "Yajilin", and K for "Kurarin". 

I initially underestimated the border-crossing rule in CTB: it turned out to be rather versatile. It can establish tighter minimal number logic for large regions and tighter maximal number logic for small regions, but also helps restrict flow in large regions.

https://pedros.works/paper-puzzle-player?W=5x5&L=(6)9(5)5&SIE=6UUUUU6URRULLUUU22LLDRR&G=tetrochain-ctb&D=2025-12-15

https://pedros.works/paper-puzzle-player?W=12x12&L=(4)1(5)2(2)4(9)4(2)40(3)4(2)4(1)20(6)4(3)6(2)10(5)6&SIE=2RRRR2RRRRDDDD4RRRRRRRRRRRR50RUR20UUUUULU5RU21UUUUUUUUUUUU6LULUUUUU4RRRR46LLLLLLLLUUUUUUUU&G=tetrochain-ctb&D=2025-12-15

When finding the compatible editors for today, I learned that the Kudamono editor for Tetrochain Y automatically supports arrowless numbers. The first puzzle below uses them.

https://pedros.works/paper-puzzle-player?W=7x7&L=(1)r6(1)4(2)r4(2)d20(5)4(5)u4&G=tetrochain&D=2025-12-15

https://pzprxs.vercel.app/p?tetrochain/12/12/m1142a1125o1135zh3125b3145zh3115o4210a1235m

Tetrochain K is a neat pairing of an established shaded cell restriction with an established clue type. Compared to Kurarin, clusters of black dots feel more relevant than clusters of white dots, since the set-based ideas can be harnessed by the area constraint.

https://pzprxs.vercel.app/p?tetrochaink/5/5/k4qck4s22h

https://pzprxs.vercel.app/p?tetrochaink/12/12/r488c888488czzx4hc8884hcr8j8j8r8j8j8t8ci48v8h8h8v8g8g8g8zzh8w

Tetrochain CTB Y K