Intermediate techniques
Start working with candidates.
Use candidates not just to solve cells, but to eliminate possibilities across the grid.
The next step
From finding answers to finding constraints.
These techniques build on the same row, column, and box logic you learned in the Beginner section. The difference is that the useful deduction may be an elimination rather than an immediate placement.
01 · Foundation
Candidate Notes
Track the values that are still possible, then use each deduction to remove candidates that can no longer be true.
Candidate Notes →02 · Intermediate
Locked Candidates
Use the relationship between a box and a row or column to eliminate a candidate. Includes Pointing and Claiming.
Locked Candidates →03 · Intermediate
Naked Pair
Two cells in one house collectively contain only two candidates, so those candidates can be removed elsewhere in the house.
Naked Pair →04 · Intermediate
Hidden Pair
Two numbers can occur in only two cells of a house, even when those cells contain extra candidates.
Hidden Pair →05 · Intermediate
Naked Triple
Three cells collectively contain only three candidates, allowing those candidates to be eliminated from the rest of the house.
Naked Triple →06 · Intermediate
Hidden Triple
Three numbers are restricted to three cells within a house, even though those cells may contain other candidates.
Hidden Triple →07 · Intermediate
Naked Quad
Four cells collectively contain only four candidates, so those four numbers can be removed from other cells in the house.
Naked Quad →08 · Intermediate
Hidden Quad
Four numbers are restricted to four cells in a house, allowing other candidates in those cells to be eliminated.
Hidden Quad →THE PATTERN
Naked and hidden are two ways to see the same constraint.
With a Naked Subset, you notice that a group of cells is limited to a group of numbers. With a Hidden Subset, you notice that a group of numbers is limited to a group of cells.
Similar to Pointing and Claiming, where these two Locked Candidate techniques are "exchangeable", Naked Subset and Hidden Subset sometimes are also "exchangeable", as you will learn from various examples in this section.