A Hidden Single emerges in cases where a digit is uniquely allowed to occupy one position on a certain house but that cell accommodates more than
one candidate and the required digit is contextually masked.
Example 1:
4, 6 and 9 could serve as filling values in R3C4 however looking deeper we find that R3C1 and R3C2 have 6 in R2C3 therefore they are useless and in
R3C6 6C6 are blocked therefore leave only the ground element 6 which has space on R3 so it is bound to avail.
Example 2:
In R6C4, the digit 3 is a Hidden Single:
Row 6 (R6): No other cell in R6 can hold 3.
Column 4 (C4) and Block 5 (B5): 3 is excluded elsewhere. Therefore, R6C4 must be 3.
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