Puzzle Description:

(This puzzle was recovered from the 2016 database crash. Description not available.)

#1: Jota (jota) on Jan 17, 2021       classify

The second ?

It took me a lot of lookaheads to figure out where things went here, and it went beyond edge logic. An interesting solve, involved enough I call it deep lookahead, unless I'm missing a shorter way. I wound up chipping away at a lot of 2's once the reds were placed.

Moderate lookahead placed the red 4's in the rows.

Look ma, no hands!

Good one, Bill!

Found to have a unique solution by wombatilim.

Found to be solvable with moderate lookahead by wombatilim.

I got to 9% with initial line & color logic; always possible there's some CL I missed but I don't think so this time.

C1: EL marks R8-9 black. L&CL to 53% and solves the red.

C20: EL marks R8 black. LL.

C2: EL marks R7 and R14 black. LL.

C19: EL marks R7 and R14 black. LL.

R20: If C4 or C17 is black, R18 is invalid. LL.

C1: If R15 is black, the 11 in C2 goes up to R4, which would make R6-7 C1 black, which is invalid. LL.

C20: Same logic as previous step. LL.

C2: If the 11 goes to R4, R14-15 C3 are black. If the 11 goes to R15 instead, R15C2 is black (obviously). Either one places the first 1 in R15, so R15 C4-8 are white. No LL.

C19: Same logic marks R15 C14-17 white. No LL.

R1: If C16 is black, R3-5 C18 are all black, which is invalid. LL.

R20: If C5 is black, R16-18 C3 are all black, which is invalid.

LL to finish.

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