3D Medusa
Simple Coloring extended across multiple digits at once — bivalue cells link candidates of different digits into the same two-color chain, unlocking more elimination rules.
The solver does not attempt this technique, so Smart Hint will never suggest it. It is documented because you may still want to spot it yourself.
How it works
- 1Medusa colours candidates, not cells. Row 1 has only A1 and E1 left for 5, so those two 5s take opposite colours — call A1's 5 red and E1's 5 teal.
- 2Each of those cells holds just two candidates, so the colour flips inside it: A1's 2 turns teal, E1's 9 turns red. Column E has only E1 and E5 left for 9, so E5's 9 turns teal — and E5's own 2 turns red.
- 3That leaves a teal 2 at A1 and a red 2 at E5, three digits away from where the chain started. A5 sees A1 down column A and E5 across row 5, and one colour is always true, so A5 can't be 2.
- 4Reference only — measured against 780 stalled Extreme positions, Medusa cracked exactly one that a rung already in the ladder didn't, so it was left out.
- First colour in the chain
- Second colour in the chain
- Cells that establish the pattern
- Where the conclusion lands
- Candidate ruled out