I am primarily a pen and paper solver

Advanced methods and approaches for solving Sudoku puzzles

I am primarily a pen and paper solver

Postby ghfick » Tue May 03, 2016 6:10 pm

I am still primarily a pen and paper solver. I like to print off blank grids and print the givens on the grids. I also like to use the 'Extended Print' option in Bernhard Hobiger's 'HoDoKu' software. You can create and print off very demanding puzzles using this software. I use grids that are about the same size as those found in the newspapers. I print four grids to a page.
My solving proceeds in four steps:
1) I solve the puzzle as far as I can without any markings. This step typically takes me up to and including 'Locked Candidates' and 'Naked/Hidden Pairs/Triples'.
2) If the puzzle is not solved, I mark all cells using the standard 'key pad' system. I do not actually print the candidates' numbers but just print a dot in the appropriate position in the cell. This step usually takes me up to and including the 'Hard' strategies [as in HoDoKu's default Hard list]. As I identify exclusions, I place an X through the appropriate dot. If the puzzle gets too cluttered with X's, I use a simple liquid paper pen to take off the X's and dots. I then continue on with the consideration of XY-Chains [although considered 'Unfair' in HoDoKu] as I am fairly good at following the possible chains of bi-value cells. I will explore a possible chain only if there is a possibility of an exclusion.
3) If the puzzle is not solved after considering all the Hard strategies and XY-Chains, I then proceed to mark the strong links. I identify the strong links by column [vertical bar |], row [horizontal bar _ ] and box [diagonal line /] to surround a dot. [The three parts to a little right angled triangle] I do not find it necessary to further mark the bi-value cells. This marking method is a composite of Andrew Stuart's method and stk's method. I do not draw lines between the two cells and, for strong links in a box, I use a diagonal line while stk uses a dot [.] With the strong links marked, I am then able to consider AICs, Continuous Nice Loops and Discontinuous Nice Loops. Even with these markings, I identify ALS-XZ and ALS-XY in a very uncertain and haphazard way. Similarly, I occasionally find the simplest of Death Blossoms.
4) If the puzzle still is not solved, I have begun the explore the world of Exocet. David P Bird's compendium on JExocet is first rate. I am just a beginner here but this pattern does seem to be within the realm of human solving. David does refer to markings that may help to identify JExocet but I have not reached that stage yet. Also on my 'to do' list are posts by David P Bird on SK Loops and Braiding.
Last edited by ghfick on Tue Jun 28, 2016 6:36 pm, edited 1 time in total.
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Re: I am primarily a pen and paper solver

Postby David P Bird » Tue May 03, 2016 10:49 pm

ghfick, what you've described pleases me as it indicates I'm not entirely alone in sticking to my 'old school' principles here. This involves treating puzzles more like a game of patience than a race or a programming challenge. My aim is to push the envelope on the puzzles that can be solved without using branching of any sort other than that needed to prove the inferences from recognisable patterns.

However there is a lot of drudgery involved in solving using paper and pencil so I use a Sudoku Drudge spreadsheet to look after the mundane stuff. This allows me to fast-forward to the challenging parts of a puzzle. Like you I have devised a personal marking scheme, GEM, which I've described < here >.

If you're a stranger to SK loops let me warn you that there have been many heated discussions here about what is and what isn't a SK Loop and the logic behind them. My attempt to put the various issues to bed, < Domino Loops (SK Loops and Beyond) >, may help you.

I'd advise you to put Braiding right at to bottom of your 'to do' list. It's a lot of effort for little gain as in modest puzzles most of the inferences provided can be found far more simply. That said, the inferences in a JExocet band nearly all result from braiding considerations, and for those who like to solve without using pencil marks, an appreciation of braiding theory is useful.

DPB
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Re: I am primarily a pen and paper solver

Postby SteveG48 » Wed May 04, 2016 1:00 pm

Hello, Ghfick. What you describe is also the way that I like to work the daily puzzles published in my local newspaper, though I prefer to work them in the paper rather than copying them out- sometimes a challenge with the small grids.

On the other hand, I also like to mix it up, using Hodoku to generate and work more difficult puzzles. A nice compromise that I also like to use from time to time is Pappocom's Sudoku program. It offers the convenience of an electronic game board without any of the automatic candidate tracking, filters, and other features that you find in the more advanced programs.
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Re: I am primarily a pen and paper solver

Postby enxio27 » Wed May 04, 2016 9:33 pm

FWIW, I solve with pencil and paper, as well. Most of my sudoku time occurs before bed (helps my mind settle down for the night) or during my son's music lessons, or in short (5-10 minute) wait times here and there. I use standard, 9x9 "vanilla" puzzles to fill the short bursts of time, but for longer periods I like to do multi-grid puzzles of various types.

I have a collection of puzzles of varying difficulty. The 9x9 puzzles are sorted (on computer) and printed (using SadMan's Sudoku program) by difficulty (as rated by Sudocue). I haven't yet reached the 9x9 puzzles difficult enough to require pencil marks, but I know I will get to those before long. With the multi-grids, I use Richard Broughton's Sudoku Solver to print the grids with pencil marks. I initially tried writing my own pencil marks, but I found it far too tedious and mistake-prone before I ever got to the fun of solving the puzzle.
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Re: I am primarily a pen and paper solver

Postby ghfick » Thu May 05, 2016 11:43 pm

David: I am adding Graded Equivalence Marking to my 'to-do' list. Perhaps such marking might help with ALS-XZ, ALS-XY and related.
I am also interested in Sudoku Drudge. I do sometimes paste a puzzle into HoDoKu, let the solver take me to the first 'Hard' strategy and then print the puzzle and markings to that point. But I also still appreciate taking a puzzle from 'first principles'.
I will keep the pursuit of Braiding in neutral for the time being.
I gather that JExocet patterns will be in play only at early stages in a puzzle. If strong link marking turns up almost no strong links, maybe one can safely proceed to JExocet consideration without a detailed consideration of AICs et al. On the other hand, with almost no strong links, such an investigation will be short lived anyhow.

Steve: I do the 5 Star and 6 Star 'Universal Sudoku Puzzles' from our newspaper most nearly every week. I do try to solve them with no markings at all as a decent brain stretch. I will have a look at the Pappocom software.

enxio27: We do not get the multi grids in our newspaper but I do see them from time to time. Definite fun. I know of folk who like Killer Sudoku. I have played with them a bit but always return to the 'classic' Sudoku. Like you, I go to puzzles of varying difficulty. Currently, I generate puzzles using HoDoKu and all the defaults except that with XY-Chains set as 'Hard' and I expand Hard to the 3000 / 5000 HoDoKu range. This setting results in puzzles with paths needing lots of XY-Chains. Also yielding nice brain stretches.

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Re: I am primarily a pen and paper solver

Postby SteveG48 » Thu May 05, 2016 11:58 pm

ghfick wrote:Steve: I do the 5 Star and 6 Star 'Universal Sudoku Puzzles' from our newspaper most nearly every week. I do try to solve them with no markings at all as a decent brain stretch. I will have a look at the Pappocom software.

enxio27: We do not get the multi grids in our newspaper but I do see them from time to time. Definite fun. I know of folk who like Killer Sudoku. I have played with them a bit but always return to the 'classic' Sudoku. Like you, I go to puzzles of varying difficulty. Currently, I generate puzzles using HoDoKu and all the defaults except that with XY-Chains set as 'Hard' and I expand Hard to the 3000 / 5000 HoDoKu range. This setting results in puzzles with paths needing lots of XY-Chains. Also yielding nice brain stretches.


I used to avoid PMs as well until forced into it, but more and more I find myself adding PMs even on easier puzzles. It often makes them go faster, and who wants to waste time on simple stuff?
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Re: I am primarily a pen and paper solver

Postby Leren » Fri May 06, 2016 12:41 am

Hi Gordon, if you want to practice finding Exocets, here is a list of puzzles that contain them. Be warned though, they are some of the most difficult puzzles, so you might have trouble solving them completely, but you will at least get practice finding the Exocets. The list tells you where they are, and their base digits.

Hidden Text: Show
98.7.....7.....6....6.5.....4...5.3...79..5......2...1..85..9......1...4.....3.2.;1;GP;champagne dry;1;r3c1 r3c2 r2c4 r1c7 1234;;
.......39.....1..5..3.5.8....8.9...6.7...2...1..4.......9.8..5..2....6..4..7.....;3;tax;Golden-Nugget;1;r1c7 r2c7 r4c8 r7c9 1247;;
.2.4...8.....8...68....71..2..5...9..95.......4..3.........1..7..28...4.....6.3..;4;elev;3;1;r5c1 r6c1 r1c3 r8c2 1367;;
..3..6.8....1..2......7...4..9..8.6..3..4...1.7.2.....3....5.....5...6..98.....5.;6;elev;2;1;r8c1 r8c2 r9c6 r7c8 1247;;
1.......9..67...2..8....4......75.3...5..2....6.3......9....8..6...4...1..25...6.;7;elev;15;1;r6c5 r6c6 r4c3 r5c8 1489;;
1....6.8....7..1........5.6..9.4.....7.2...3.8....76..3....1..5.4.9.......2.7....;8;elev;16;1;r2c8 r3c8 r6c9 r7c7 2479;;
.2...67..4...8......93........9..57..1...7..2......61.3...4..6...8.......6...5.2.;9;tarekdb;tarx0075;1;r4c9 r6c9 r1c8 r9c7 3489;;
98.7.....6...5......4..93..5......6..7..8......9..24....1.....4....9.1.......1.32;11;GP;H1;1;r8c8 r8c9 r9c3 r7c6 5678;;
...4...89..7..92......3...526...1.....19.....7.....1..5...9..4...6..29.....8....3;15;elev;17;1;r5c1 r5c2 r6c6 r4c7 3458;;
........94....92......7..45..1.3.....7.6..9..8....7..2.3.7..8....6.1....9....5.2.;16;elev;18;1;r1c7 r3c7 r6c8 r9c9 1367;;
...4...8...7..92......3...526...1.....19......7....1..5......4..1.8....3..6..29..;19;elev;9;1;r5c1 r5c2 r6c6 r4c7 3458;;
.....6.8....1..2...9..7...5..5.4...734...8...97.........9...6..7...3...4...2...1.;30;elev;5;1;r5c3 r6c3 r3c1 r8c2 1268;;
..3..6.8....1......9..7...4...8..6..3...4...2.....5.1...2.9...37........94....5..;33;elev;6;1;r8c3 r9c3 r3c1 r5c2 1568;;
.2.4..7...5...9.3.6...7......5..8.9.7...2.....4.6..3.......1..85......1...1...9.3;34;elev;8;1;r8c7 r8c9 r7c3 r9c6 2467;;
98.7.....6.....9....5....7..4..3..2...85..4.......4..1..69..5......2...3.....1.4.;35;GP;H4;1;r3c1 r3c2 r2c4 r1c7 1234;;
98.7.....76....9....5......4...6..3...75..6.......2..1..86..5......1...2.....3.4.;36;GP;H5;1;r3c1 r3c2 r2c4 r1c7 1234;;
1...5...9..7...2...69..3.4....8........91..7.9....5..83..5....1..2...6...4.......;37;elev;34;1;r4c6 r5c6 r1c4 r7c5 2467;;
98.7.....6.....7....7.5....5....4.3...89..5......2..1..3.....4...98..6......1...2;44;GP;H7;1;r3c1 r3c2 r2c4 r1c7 1234;;
..3..6.8.4..7......9..3.....3.....15..5..18.........6.3..9..2...7..4......2..5..1;48;elev;L3;1;r4c7 r6c7 r1c9 r9c8 3479;;
...4.67....67.9.......1......9.6.4..5......2..8......33......5...4.9.1...1...2..8;53;elev;H2;1;r3c4 r3c6 r1c3 r2c7 2358;;
..1...5...2.4...6.3....7....6.28........9..2.......4.65.....1...9.8...4...7.....3;54;col;H2;1;r6c5 r6c6 r5c2 r4c8 1357;;
...4....9....8.2..6....3.1..1...7...7..6..5...3.....7.3....5.2...29..8......2...4;56;elev;32;1;r5c2 r5c3 r6c6 r4c8 2489;;
1...56.....71.......9....1..4..6.3.......8..29..7...6......24..5..6...9.....3...8;59;elev;33;1;r1c2 r1c3 r3c4 r2c8 2348;;
....56.8..5.7....3..8......2.....9...4.5....7....92.6.3.4.....15..1..4...1.....7.;61;elev;31;1;r9c1 r9c3 r7c4 r8c9 2689;;
...4...8...7..92......3...526...1.....19.....7.....1..5......4...6..29..9..8....3;64;elev;20;1;r5c1 r5c2 r6c6 r4c7 3458;;
.2.45....4....92....6.2............83...9.5...7...3.1.5..9..3...8......6..1....7.;66;elev;24;1;r1c6 r3c6 r5c4 r7c5 1678;;
1....6.8..5....2....9.....4.....86.33...7........1..7..4.9.....8....7.6...2...5..;67;elev;L6;1;r4c4 r4c5 r6c1 r5c8 2459;;
1....67...5.7....3..8.....4.4.5..3......2..9........45.7.9...3.6...1......2..8...;69;elev;28;1;r5c7 r6c7 r2c8 r7c9 1268;;
...4....9.5...9.3.......1.52..8.......6.4.....1...53....42...7.8...67....7......3;70;elev;19;1;r1c8 r3c8 r6c9 r9c7 2468;;
1...5..8...7.....6.8.3..5..2......1...6.....7.9...38.....9.4....4..3.9.....8...2.;73;elev;58;1;r7c5 r9c5 r3c6 r6c4 1267;;
.2..5.7...56.....37....3...2...3...5...1...9..69...........481.6...7...2.4.8.....;79;elev;59;1;r3c2 r3c3 r2c5 r1c9 1489;;
...1....9.......85..9.5..6...5.3...6.7...2...1..4.......3.8..9..2...73..4........;82;col;H3;1;r1c7 r2c7 r4c8 r7c9 1247;;
.......35.....2.6...3.5..8...5.9...6.7....9..1..4.......6.8..9..2.1.....4....7...;83;col;H4;1;r1c7 r2c7 r4c8 r7c9 1247;;
1....6....571......9..7..1...8...........89.29..5...6.....42..3.3....4..7..6...9.;84;elev;61;1;r1c2 r1c3 r3c4 r2c8 2348;;
.......894....92.....7...4..35.7......651....8....2....7..6.5..5....7..8..13.....;85;elev;62;1;r1c7 r3c7 r6c8 r6c9 r8c8 1367;;
....5..8...67..1.......3..426.9.............19.7...2...3..4..1......8..5..21..6..;92;elev;41;1;r5c1 r5c2 r6c4 r4c7 3458;;
..3..67...5..8.....9.1.........9..1...7..32..8..5...4.37....4.......4..6..4....72;94;elev;47;1;r7c8 r7c9 r8c3 r9c6 1589;;
..3.5.7..4....9....8.2.....2......4..9.8.......1.6.5.....5.16......7...3..6....57;95;elev;48;1;r7c8 r7c9 r8c3 r9c5 2489;;
98.7.....6.....9....5....7..4..3..2...98..4.......4..1..65..8......2...3.....1.4.;97;GP;H9;1;r3c1 r3c2 r2c4 r1c7 1234;;
98.7.....6.....7....7.5.....4.....3...98..4......24..1..89..6......1...2.....3.4.;104;GP;H13;1;r3c1 r3c2 r2c4 r1c7 1234;;
.....6.8....1..2...9..3...52.....1...3..9...77..8...6...5.....4.7.3.4...9...7....;106;elev;50;1;r8c1 r8c3 r7c5 r9c9 1268;;
..3.....94....91......3.54....6.....3...9...1.7...2.6...29..8....8..7...9...4...5;110;elev;52;1;r1c7 r1c8 r3c1 r2c5 2678;;
98.........79..6......5....7..4..9....6.3..2......5..1.7.5..8....4.1..5......2..3;118;GP;H11;1;r1c3 r3c3 r4c2 r7c1 1235;;
1....6.8....18.2...9..7.......7....37...6..1...9..54...4......25..6...7...1...3..;120;elev;39;1;r2c6 r3c6 r5c4 r8c5 2349;;
....5..8...67..1.......3..42.....9....9..7...61.9..........8.3...1.7.6...3..4...5;121;elev;35;1;r5c1 r5c2 r4c4 r6c7 3458;;
98.7.....6.....8....7....5..4..3...2..96..4.......4.1...85..6......1..4......2..3;127;GP;H17;1;r3c1 r3c2 r2c4 r1c7 1234;;
....5...9..71..2.......3.4.2....86..87.6.......6.1......28..1......4...3.9...1.5.;128;elev;111;1;r6c1 r6c2 r4c4 r5c7 3459;;
1......8..5......6..93..4...7......18......5...4.2.6.....26...7...93......2..43..;129;elev;113;1;r7c6 r8c6 r3c5 r6c4 1578;;
..34......5...9...6...2.1..2...6...1.4.5...6...6..3.....9...6.7......8.28...7..1.;130;elev;112;1;r7c8 r8c8 r3c9 r4c7 3459;;
..3.5.7..4....9....8.2.....2....5.4..9.8.......5.1.3.......16....65....3....6..75;131;elev;115;1;r7c8 r7c9 r9c3 r8c5 2489;;
..3.5.7..4....9....8.2.......5.1.6.......4.2.9..8....737....5....6.....1....3...6;132;elev;114;1;r7c8 r7c9 r9c3 r8c5 2489;;
98.7.....6.....7....7.5.....4..9..3...85..9.......2..1..69..8......3..4......1..2;134;GP;H18;1;r3c1 r3c2 r2c4 r1c7 1234;;
....5...9.5.1...3.....37...2..6..8...6..1..7...4..5.....9.....2.3...1.6.8.....4..;136;elev;117;1;r1c4 r3c4 r5c6 r8c5 2489;;
.....6......18.2.66..32.....7.....5...9...4..8....2..33....1..8..5...9......4.37.;137;elev;116;1;r1c4 r1c5 r2c1 r3c9 4579;;
.2..5......67..1..7....3..4..56.....3....7..8.17.2............7.....489.9.....34.;138;elev;119;1;r7c7 r7c8 r8c1 r9c6 1256;;
.23.5.....567....27...........9.4.1.3...6...7.1....9..5...2...6.....84...38......;139;elev;120;1;r3c2 r3c3 r2c5 r1c9 1489;;
1....6..9....8..3...82..4.....6.4.....5.2.6...7.5......3......1..4..25..9......7.;143;elev;121;1;r4c5 r6c5 r3c6 r8c4 1379;;
...4..78......92..6...7...1.6..1...53..........5..84...3.....2.71.9.......6.3...7;145;elev;118;1;r7c3 r8c3 r3c2 r4c1 2489;;
.2...67..4...8..3....2.............53...4..1...5..76...34..8.9..81.9.4..9........;146;elev;122;1;r9c2 r9c3 r7c5 r8c8 2567;;
1..4..7...5......6..8.3..1.....9.1......289....93...2..6....5..7.......1..2..3.4.;147;elev;124;1;r4c4 r5c4 r3c6 r9c5 1567;;
1....6.....71..2...8..3...12.....1...3..9...8..6....7.....4.8...4.3..9.....9.5..4;149;elev;123;1;r7c4 r7c6 r9c2 r8c9 1267;;
..3..67...5.1....66...2..4..8....9..3.18.......5.....8.....4.2..3.9....1....7.6..;150;elev;125;1;r4c1 r4c3 r6c4 r5c9 2467;;
.2..5.7..4....9.....8....1...1....4..6..3.5..9.......8....6..57...2..3...7.3.5...;151;elev;H4;1;r7c4 r7c6 r8c2 r9c7 1489;;
.....6.8....1.9..6.6..3.1..2.......87......5..1.3..4....8.4...25......7..9...38..;152;elev;126;1;r1c5 r2c5 r6c6 r9c4 2578;;
9876.....65....7...........5...4..3..2......1..68..5....59..8......3..2......1..4;153;GP;H21;1;r3c1 r3c2 r2c4 r1c7 1234;;
98.7..6..7..........5.4..7.3.....9...6......8..7..4.5...24...1.....2...3....15...;154;GP;H19;1;r8c4 r9c4 r3c6 r6c5 3689;;
1....6....571.......9...51..4....3.......8..29..7...6......24..5..6...9.....3...8;155;elev;129;1;r1c2 r1c3 r3c4 r2c8 2348;;
12..5.....5......6..6..3.....1.6...8.8.9...7......84.....7..8.......4.9...2.3...5;156;elev;H5;1;r3c1 r3c2 r2c5 r1c9 4789;;
98.7.....6...9.7....7..5...4......3..3...2..1..95..8....68..5.......1.2.........4;157;GP;H20;1;r3c1 r3c2 r2c4 r1c7 1234;;
.2...6..94..18......8...4.........5...15...9..6...3..2..26....7.7..3.9.......7.3.;158;elev;128;1;r7c7 r7c8 r9c2 r8c6 1458;;
...4.....4...891...9..31........5..6.8.3..4..6.7....5..1.9..8....2......9...2...7;159;elev;127;1;r1c5 r1c6 r2c2 r3c7 2567;;
98.7.....76....5....5.......9..4..3...85..6.......2..1..98..7......3..2......1..4;160;GP;H22;1;r3c1 r3c2 r2c4 r1c7 1234;;
.2.4...8.4.7..9...6.8......2..6...4.....459......1...3..27...6.........1.6..3.5..;161;elev;130;1;r2c2 r3c2 r4c3 r7c1 1359;;
1....6....5.7....3..9.2.....4.5..3......9..5........74.7.8...4.6.....8....2..1...;163;tarekdb;Silver_Plate;1;r5c7 r6c7 r2c8 r7c9 1269;;
98.7.....6.....5....5....97.4..3......98..7.......2.1...86..9......4...2.....1.3.;164;GP;H23;1;r3c1 r3c2 r2c4 r1c7 1234;;
.....678....1....6.6..7.4...7...1..4..5.2....9...3....3.....5...1...7..8..29...4.;167;elev;131;1;r2c7 r2c8 r1c2 r3c6 2359;;
98.7.....76....8....5......4...3..7...68..9.......2..1..79..5......4...2.....1.3.;169;GP;H24;1;r3c1 r3c2 r2c4 r1c7 1234;;
.2.4.6.....6.8.2..7....2....3.....9.5.......7..1..48....26..1...9..1..5.........3;170;elev;H6;1;r1c5 r3c5 r6c4 r7c6 3579;;
..3..6..9.5.1.....8...7.........436...4...9.....62...4.1.8.......6..2..37...6..5.;171;elev;99;1;r6c7 r6c8 r4c3 r5c6 1578;;
98.7.....6...8.7....7..5...4......3...89..6.......2..4.3...1..2..95..8.........1.;173;GP;H25;1;r3c1 r3c2 r2c4 r1c7 1234;;
98.7.....76....5....5.6.....4.....3...98..6.......2..1..79..8......1...4.....3.2.;180;GP;H27;1;r3c1 r3c2 r2c4 r1c7 1234;;
1....6....5.7....2..9.3...4...5......7...1.....8.9.3..6.....4.8..2.4..9.......2.3;181;elev;103;1;r7c8 r9c8 r3c7 r6c9 1567;;
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Re: I am primarily a pen and paper solver

Postby David P Bird » Fri May 06, 2016 7:01 pm

Gordon,
you wrote:I gather that JExocet patterns will be in play only at early stages in a puzzle.

That can be true but not always. JE inferences that were unavailable at the start may come into play later after other eliminations have been made when they can considerably shorten a solution.

David
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Re: I am primarily a pen and paper solver

Postby enxio27 » Sun May 08, 2016 2:29 am

ghfick wrote:enxio27: We do not get the multi grids in our newspaper but I do see them from time to time. Definite fun. I know of folk who like Killer Sudoku. I have played with them a bit but always return to the 'classic' Sudoku. Like you, I go to puzzles of varying difficulty. Currently, I generate puzzles using HoDoKu and all the defaults except that with XY-Chains set as 'Hard' and I expand Hard to the 3000 / 5000 HoDoKu range. This setting results in puzzles with paths needing lots of XY-Chains. Also yielding nice brain stretches.


Other than Samurai (5-grid) puzzles, most of the multi-grid puzzles in my collection are from sites that no longer exist, such as Ruud's Sudocue.net and djApe's site. (I collected all of the specialty puzzles from Ruud's site and reposted them here: http://forum.enjoysudoku.com/ruud-s-specialty-puzzles-t31546.html If you enjoy the Clueless Specials, Clueless Explosions, and Samurai, I have those, as well, although not currently online.) There is another site I discovered fairly recently, vfalcone.ru, but you have to complete one puzzle before you can access the next. It has standard 9x9, Samurai, and Ninja (11-grid) puzzles. It will probably be a long time before I run out of puzzles and have to generate more using one of the programs I have.

I do a killer sudoku every now and then, but I prefer puzzles that use straight logic rather than those that also incorporating mathematics. I use sudoku primarily to relax and to tire my brain out before bed so that I can sleep. To me, killer sudoku is not relaxing.

It sounds as though your solving skills are considerably farther advanced than mine. I'm still trying to wrap my head around XY-chains.
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Re: I am primarily a pen and paper solver

Postby ghfick » Mon May 09, 2016 1:45 am

Steve: I do agree, in principle, about efficiency. I still have this grey zone when its comes to when I should markup. David refers to the Drudge. Marking up a puzzle is 'character building'. Sometimes I lose patience with a puzzle that appears to be elementary but the puzzle will not fall. Then, when I mark it up, I see that I missed a Naked Triple and I am a bit humbled. So, setting completely unnecessary constraints is part of the fun. Occasionally, for me, an aspect of a puzzle is seen that might be missed if a more structured [efficient?] approach had been applied.
Leren: Your JExocet list is soon going to occupy a considerable amount of my Sudoku time. Using David's Compendium, I now have a grasp of the pattern. Next, I will test myself with puzzles in your list. Then, I will enter the challenge of attacking puzzles that 'might' contain JExocet. Then, it is about adding the pattern to my lexicon. Maybe, at some future time, there will be the joy of identifying a JExocet without any 'help' at all. [well down the road for me]
David: Your compendium currently dominates my Sudoku time. It will be interesting to see puzzles with a late(r) arrival of a JExocet.
enxio27: Thanks for the link. Please do repost the others to keep them in action. Up until quite recently, I saw XY-Chains as too daunting. I first saw the alternate logic to place the XY-Wing as the simplest [shortest] XY-Chain. Then, I used the preferences in Hodoku to create puzzles with short XY-Chains [go to Steps and change the chain length from the default]. I practiced these short ones for a while. Then, I read:
https://sysudoku.com/2011/12/06/xy-web/
I have not been to incorporate 'XY Railroads' into my approach, but this post did enable me to see the chain's length as just a descriptor and not a obstacle.

Best
Gordon
Last edited by ghfick on Tue Jun 28, 2016 6:40 pm, edited 1 time in total.
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Re: I am primarily a pen and paper solver

Postby enxio27 » Mon May 09, 2016 2:32 pm

ghfick wrote:enzio27: Thanks for the link. Please do repost the others to keep them in action.

Now that I think of it, all of Ruud's Clueless Specials, Clueless Explosions, and Samurai have been reposted to Richard Broughton's Sudoku Solver forum by one of the admins there, along with many others that have been created since then by forum members. There is a forum section devoted to each of those three puzzle types, as well as one for killers, one for other gattai (multi-grid puzzles) and another for other variants (jigsaw, windoku, anti-chess, etc.).

Up until quite recently, I saw XY-Chains as too daunting. I first saw the alternate logic to place the XY-Wing as the simplest [shortest] XY-Chain.[/quote]
I still haven't gotten the hang of XY-Wings yet. I guess that's next on the list. Thanks for the suggestion and the link!
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Re: I am primarily a pen and paper solver

Postby ghfick » Thu May 19, 2016 10:47 pm

I have attached two files. One shows the strong links with the components of a little triangle using a file developed by John Welch. [sysudoku.com] The other is an actual handwritten puzzle near completion [using the little triangles]
Attachments
DSMM_15_triangle.png
DSMM_15_triangle.png (76.73 KiB) Viewed 297 times
DBL.png
DBL.png (45.41 KiB) Viewed 297 times
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