Learn how Locked Candidates (Pointing and Claiming) work to eliminate candidate numbers across rows, columns, and 3x3 blocks.
Locked Candidates occurs when candidate numbers for a specific digit within a 3x3 block are restricted to a single row or column. Because that digit MUST go into one of those cells within the block, it cannot appear anywhere else along that same row or column outside the block.
When candidate numbers for a digit in a 3x3 block are aligned strictly in one row or column, they "point" along that line. You can safely eliminate that digit from all other cells in that same row or column outside of the 3x3 block.
Looking from the perspective of a row or column: if a digit can only appear within a single 3x3 block along that row/column, then that block "claims" the digit. You can eliminate that digit from all other empty cells within that 3x3 block.
