Practise: Cage subsets (Rule of K)
This trainer starts at the verified cage-subset position. No unrelated opening moves are needed: examine the two 5-cages and apply the technique immediately.
You begin at the right position. The selected blue cell shares a row with two 5-cages. First find their four cells, then use the hint to check the safe elimination step by step.
Your turn first
Spot the idea before the hint explains it
- 1. Look
- 2. Check
- 3. Proof
Look at the marked starting cell, cage outline and sum. Which digit or combination is forced, and what visible sum fact supports your idea?
How to spot it
Look for three or four marked cells whose sums and candidates reduce them to the same small digit pool.
Put it to use
Where you will meet it
Expert grids are the only place this pattern regularly decides the solve. Bring your notes.
Play ExpertStuck on a grid of your own?
Type the position into the solver and it walks the whole solution, naming the technique behind every step — including this one.
Open the solver