Doh. Stymied by simple hidden naked pair. Greens, no guesses. I've used a quick check for sudoku puzzles -- 41 of 81 small squares solved (more than half) usually* means it's resolvable up to a level of hard without employing greens, guesses or requiring second level pattern recognition. *(but not always for mediums or above, for those who care about skill level.) For skill level I use these simple formulae : 1. No guesses - slightly better than 50% of the animal kingdom 2. No greens - better than 75% of the population 3. 1st level pattern recognition - 115+ IQ 4. 2nd level - 120+, above 95% of all humanity 5. exotic patterns, 130+ - you're an alien, can one get your autograph?

start

done

Not so easy to see the easy stuff. 16.

Easy - one lucky guess, i guess

made a mistake, too tired - will try again tomorrow...