Changes March 2026
Due to the introduction of
Forcing Nets many Weekly Unsolvable puzzles can now
be solved. I have flagged all the Sudoku ones which are solvable. I am struggling to make any new ones so we'll
have to see if the Weekly can continue. The point of the Weekly was to provoke discussion and new ideas, so
that is progress. But my solution is unlikely to be optimal so alternatives are welcome.
Archive
Each week a new 'unsolvable' will be published and the previous will be accessible here from this archive section.
If you like very tough puzzles, these are for you.
Share and Enjoy
Supporter Members have access to all these puzzles going back to number 1.
... by: Dieter
#715 - initially populated cells: 22 = 27,2 %
No solver used, solver = brain.
basics: %
Strategy: numbers 1,3,4,5 occur most frequently, combine two cells with almost same candidates.
combinations of F3 = (1,3,5,7) and F7 = (3,4,5,8);
after basic checks 2 matrices left: 3/4 and 3/5
F3=3 & F7=5 solve with A9=1.
Optimization:
A9=1 & F7=5 solve.
... by: Norman Powell
AS's solver finds 5 eliminations by Forcing Network, these are indicated in the following description. The order they are found is different.
Solved by Forcing Networks and Complimentary Forcing Networks:
Forcing Networks Pass 1:
Eliminate 2F1 [1st Found by AS], 5F3, 2G5 [2nd Found by AS].
Forcing Networks Pass 2:
Eliminate 9A5 [4th Found by AS], 2B6 [5th Found by AS], 7C9, 3D1, 2E6, 6F1, 6F4 [3rd Found by AS, last to be found in this ordering], 3F7, 8F7, 4H8.
3D Medusa Rule 3: Both Colours in Cell H1, eliminate other possibilities.
Confined to Box: 2 is confined to Row 7 and Box 7, eliminate other 2's in Row or Box.
Forcing Network Pass 3:
Eliminate 3A3, 3A4, 8A5, 3A6, 1B2, 5B5, 8B5, 3B6, 6B6, 7B6
Complimentary Forcing Networks: Possibilities Forced to Same State when Value 6 in Cell C1 is ON or OFF - Eliminate: 6D2, 6D5, 6D9
Eliminate: 8C2, 8C5, 8C7,
1D2 has to be ON, eliminate other possibilities in D2
Eliminate: 2D2, 6D2, 9D2, 1D5, 2D5, 6D5, 6D9, 6E2, 9E4, 9E6, 1F2, 1F3, 7F3, 1F4, 2F4, 7F4, 8F4, 1F5, 7G2, 9G2, 1G5, 9G5, 1G9, 3G9, 8G9, 5H3, 1H4, 9H6, 8H7, 9J5, 6J9.
Completed with five passes through solved cells.
... by: Frans Goosens
#715
With trial and error
Combination A1=347 and I9=367
************************************************************
A1=3 I9=3 No solution, Fixed
Combination 2-digits cells
C1=4 ( F1=7 ) Solved,
Total solving time is : 15 sec.
Number of logical steps is : 1374
... by: Serban
# 715 Basics to 22
1. B7=8 & C7=7 solve
2. A8=9 & E8=4 solve
3. C4=8 & C7=7 solve
4. E3=5 & H8=1 solve
