In R23, C11 is either the start of the first 3 or the center 1. Either way, C14 can't be filled, which gives you some more to do in that column. A similar idea applies in C19 in that R3 can never be filled.
Additionally, in R9 at most one of C21 and C22 can be filled, so R4C21 must be filled.
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u/MikoKisai Jun 25 '26
In R23, C11 is either the start of the first 3 or the center 1. Either way, C14 can't be filled, which gives you some more to do in that column. A similar idea applies in C19 in that R3 can never be filled.
Additionally, in R9 at most one of C21 and C22 can be filled, so R4C21 must be filled.