22 December 2022

Fear

That I had previously lost all four games against this opponent may have contributed to my error at the end.

White to move
In a game 10 with three minutes remaining, it took me thirty seconds to find the only move that doesn't lose.

61.Re3+ Bxe3??

61...Kxe3 62.Kxg2 draws

62.f8Q+ Bf8 63.Qxf4??=

Either 63.Qa8+ or 63.Qa3+ would have won.

63...Kxf4 64.Kxg2

We played until Black captured my last pawn.

I used one second each for my moves after 61.Re3+. When I have three minutes remaining, there is no need to rush moves towards a draw.

07 December 2022

Wrong Bishop

When my opponent blundered to give me a knight fork, I saw a clear route to a draw.

White to move
46.Nc1+ Kb2 47.Nxa2 Kxa2 48.f4=

The engine suggests that White can play for advantage with 48.Rd1 Bc5 49.Rc1 Bb4 50.Rc7 a3 51.Rxh7 Kb2 52.Ra7 White's active king and three to one pawn majority more than compensates for Black's bishop, although this, too, should be drawn.

My plan was to exchange off Black's g-pawn and assure myself of reaching an ending where Black's bishop cannot guard the promotion square of his remaining pawn.

49.g4 a3 50.f5

Black to move
Only after the game, did I give any thought to how Black might have disrupted my plan.

50...gxf5 

This exchange gave me the draw that I sought. However, Black could try 50...g5 51.f6 a2 52.f7 Bc5 53.h4 again seeking to leave all Black's pawns on the h-file. 53...h6?? 54.hxg5 hxg4 Black's bishop will prove to be overworked after White's king mows down the g-pawn.

51.gxf5

Black to move
My after school chess club saw this position on Tuesday. They were asked how play might proceed and what should be the result. One student identified that the bishop does not control the promotion square for the h-pawn.

51...a2 52.f6 Bxf6 53.h4 a1Q 54.Rxa1 Bxa1 55.Kh1 Bf6 56.h5 h6 57.Kg2 Kc4 58.Kh1 

Post-game analysis with Stockfish set at a depth of 18 plies on chess.com produced a comic evaluation.

Black to move
Posting this position in social media with the comment, "Stockfish is wrong. This is a dead draw", elicited a lot of comments. Some posters revealed that they do not know this elementary endgame. Others sought to explain it to them.

White's pawn is of no consequence. Black cannot evict the White king from h1. The king will shuffle between h1 and any of the adjacent squares until these are taken away. My opponent played it until stalemate.






25 November 2022

Advanced Chess Camp

Tomorrow, I am conducting the advanced group at Inland Chess Academy's Turkey Camp. The relevant portion of the flyer is pictured below.

Students will be given a short quiz so that I can determine how fast or slow to move through elementary pawn endings before we get into the heart of the session. I gathered a lot of training and study materials from databases of youth games. One benefit of nearly two years of online youth tournaments due to COVID was that I now have many more games played by local youth, and also the databases from two years of state scholastic championships.

These are a few of the positions that I have selected.

White to move

Black to move

White to move

White to move

Black to move






20 November 2022

The Same Old Story

Yesterday I was the pairing director for a youth tournament with 51 players. 28 were playing in their first tournament. I've run pairings for at least 120 such events, but this one had the largest number and highest percentage of unrated players in my memory. Naturally, a fair amount of time was spent teaching some basic rules and elementary skills.

As with a much smaller event two weeks ago, there were unnecessary draws among players who have not yet learned basic checkmate skills (see "The Difference"). In one game, I counted moves for players who were not recording their game. The player with the advantage told me that she did not know how to checkmate with rook and king against king. I asked whether she thought she might do so accidentally. She said that was her hope. She came close.

After 45 moves, this position was reached.

Black to move
45...Re1+

After this move was played, Black was no longer able to force checkmate before the fiftieth move was reached. The fifty move rule states that a game is drawn when fifty moves are played without a capture or a pawn move. The last capture took place before I was at the side of the board and counting.

I declared the game a draw after my count reached fifty. Then I showed the players how Black could have won.

Had Black played 45...Kf3, White probably would have played 46.Kd1. A similar arrangement of the pieces had occurred several times prior as Black slowly managed to persuade White to retreat his king from the 6th rank to the first rank. That none of this retreat was forced highlights that some attention might be given to proper defensive play as well.

Black to move
Six of Black's possible moves lead to checkmate on the next move: Re3, Re4, Re5, Re6, Re7, and Re8. I showed the last one to the children. Then 47.Kc1 is forced and 47...Re1 is checkmate.

Had Black played 45...Kc3 from the initial diagram, White's best move would be 46.Kb1.

Black to move
Checkmate can be forced in three with ten different Black moves from this position. Black's rook can move anywhere on the e-file or anywhere to the right (left from Black's side of the board) on the second rank.

One possibility: 46...Re3 47.Ka2 Re1 48.Ka3 Ra1#.

It behooves chess teachers to teach these elementary checkmates to children.

See also "Lesson One" and "Teaching Elementary Checkmates".



17 November 2022

Greco on 2...Qf6

Gioachino Greco's explorations of an inaccuracy common among beginners deserve attention. This post does that, as promised in "How Bad is 2...Qf6?" Greco's games with 2...Qf6 all begin: 1.e4 e5 2.Nf3 Qf6 3.Bc4 Qg6 4.O-O Qxe4 5.Bxf7

Black to move
Greco's explorations of this queen foray appear in the Paris (1625) and Orléans (n.d.) manuscripts. Peter J. Monté notes in The Classical Era of Modern Chess (2014) that Orléans was likely copied from the Paris MS (339), although some errors were corrected. Part II of this book, "Openings and Games of the Classical Era of Modern Chess" (439-530), has been an indispensable resource.

I have contended that Greco's games are poorly known, even by those who think they have studied all of them. Most players access these games through ChessBase or websites such as chessgames.com (currently 90 games). The latter has more Greco games, but both offer shorter versions of what is available in such old books as "Professor Hoffmann" [Angelo Lewis], The Games of Greco (1900), and William Lewis, Gioachino Greco on the Game of Chess (1819). These shorter versions miss the best of Greco's analysis.

A couple of years before the earliest version of what eventually became ChessBase Mega, David Levy and Kevin O'Connell made an effort to record all known games up to 1866 in Oxford Encyclopedia of Chess Games, Volume 1 1485-1866 (1981). They offer 77 Greco games, many annotated. These are extracted from Hoffmann's text. As with Lewis before him, Hoffmann buried the best analysis in the variations, which sometimes are much longer than the main game. Levy and O'Connell continue this practice.

The games in ChessBase come close to representing these abbreviated "main games" sans the variations. If the longest variation of each game were the main game instead, what most chess players know of Greco would be substantially enriched. Here I offer improved versions with notes. The notes show other lines that appear in Greco's manuscripts and in Hoffmann.

Greco,Gioachino [C40]
Paris, 1625

1.e4 e5 2.Nf3 Qf6 3.Bc4 Qg6

ChessBase Mega 2020 has four games with this move. Three are Greco's. The other was a fighting draw played in Germany in 2010. No rating is given for the player of Black, while White's is slightly over 2000.

4.0-0 Qxe4 5.Bxf7+

All of Greco's games reach this point. The analysis continues with lines that follow all three of Black's legal moves.

5...Kd8

5...Kxf7 6.Ng5+ Ke8 7.Nxe4 matches a game in CB Mega 2020 and also appears in the Paris MS.

White to move
6.Nxe5 Nf6

6...Qxe5 7.Re1 Qf6 8.Re8# Orléans. Game XXI, var. A in Hoffmann. This line ends with the same checkmate that can be found in one of the Greco selections in CB Mega 2020.

7.Re1 Qf5 8.Bg6

Black to move
8...Qe6

8...hxg6 9.Nf7# Game XXI, var. B in Hoffmann; Paris and Orléans MSS.

9.Nf7+ Ke8 10.Nxh8+ hxg6 11.Rxe6+ dxe6 12.Nxg6 1-0

Black to move

This game and its variations appear in Paris MS (1625) XXXIII; Orléans MS XXII. The game is XXI, var. C in Hoffmann.

Greco,Gioachino [C40]
Paris, 1625 

1.e4 e5 2.Nf3 Qf6 3.Bc4 Qg6 4.0-0 Qxe4 5.Bxf7+ Ke7

White to move
Greco considers every legal move for Black after the bishop check.

6.Re1 Qf4 7.Rxe5+

Black to move
Here, also, Greco considers every legal move for Black.

7...Kxf7

7...Kd8 Paris MS (1625) XXXIV. 8.Re8# This game appears in ChessBase Mega 2020.
7...Kf6 8.d4 Qg4 9.Bh5 Paris MS XXXIV.
7...Kd6 8.Rd5+ Kc6 9.Nd4+ Paris MS (9.Ne5+ Orléans MS)

8.d4 Qf6 9.Ng5+ Kg6 10.Qd3+

Black to move
10...Kh5

10...Kh6 11.Nf7# is given as the main line in Levy and O'Connell. Hoffmann, game XXII.

An essential aspect of Greco's technique in dealing with the horrid positions for which he is well-known is to seek to improve the losing side's defenses. When only the shortest versions of these games are known, this technique is hidden. 

11.Nf7+

11.g4+ is not attested by Monte, but is found in CB Mega 2020.
11.Nf3+ Kg4 (11...g5 12.Rxg5+) 12.h3# Orléans MS.

11...Kg4

11...g5 12.Rxg5+ Game XXII, var. B in Hoffmann.

White to move
12.h3+

Hoffmann writes, "Greco gives this move as mate, but this is obviously a slip, Black still having one square available" (65). Monte notes this error in Paris XXXIII (477).

12.Qg3# Monte notes that Greco overlooks this mate.

12...Kh4 13.Qg3# 1-0

This game appears in the Paris MS (1625) XXXIII. Also as Game XXII, var. A in Hoffmann.

Greco,Gioachino [C40]
Orléans, 1625

1.e4 e5 2.Nf3 Qf6 3.Bc4 Qg6 4.0-0 Qxe4 5.Bxf7+ Ke7

5...Kxf7 6.Ng5+ Ke8 7.Nxe4 is found in CB Mega 2020

6.Re1

Black to move
6...Qf4 7.Rxe5+ Kd6

7...Kf6 8.d4 Qg4 9.Bh5 Game XXIII, var. A in Hoffmann.
7...Kd8 8.Re8# Paris MS (1625) XXXIV; Orléans MS. Game XXIII in Hoffmann. This version is in CB Mega 2020.

8.Rd5+ Ke7 9.Qe1+ Kxf7 10.d4 Qf6

White to move
11.Ng5+ Kg6 12.Qe8+

Paris MS has an error here, corrected in Orléans.

12...Kh6 13.Nf7+ Kg6

White to move
14.Nxh8# 1-0

This game appears in the Orléans MS. Also Game XXIII, var. B in Hoffmann.

My view is that Greco's attacking technique against the best defense he found for Black is quite instructive. Of course, 2...Qf6 is a bad move, and 3...Qg6 is worse. Nonetheless, the simple refutations offered in the sample of these games in ChessBase Mega and on database websites have unjustifiably tarnished Greco's reputation. Much more of value exists in his model games than is generally believed.

16 November 2022

Decisive Advantage

My students this week are seeing a series of positions in which White has a decisive advantage. Before suggesting moves, or seeing those that were played, I ask them to assess the position. What features account for White's substantial advantage?

The intent is for them to grow in their understanding that a player must use all their pieces in coordination. They should notice that in each position, White's pieces are more mobile, offer concrete threats, and work together. Students are also asked to understand the difference between the pieces on the board and the pieces in the battle. This dynamic imbalance is temporary unless the player wit the advantage acts with vigor.

I spent about an hour gathering 16 positions for these lessons, but no student so far has seen more than eight. The first two are from famous games that many of the students have seen before.

The first is from Paul Morphy's Opera Game.

White to move
The second is from Gioachino Greco's best known use of the Greco Attack (see "Cultivating Error"). I have had this position myself in at least 17 games, winning 16. The one loss was a bullet game where I inexplicably put a horse on a square earmarked for an elephant.

White to move
The third position highlights the relationship between space and mobility. It comes from a game that I played on Chess.com a few days ago.

White to move
Number four was presented at "Desperation". It highlights concrete checkmate threats. Number five is a textbook endgame exercise.

White to move
The sixth proves difficult for students to assess. It comes from a cyborg game played in a match organized by the International Correspondence Chess Association (ICCF). In this game, White used his intuition and a great deal of time on moves 13-15 to acquire mobile center pawns that confer a dynamic advantage.

White to move
Thomas Engqvist's analysis of Morphy,P. -- Morphy,A., New Orleans 1849 in 300 Most Important Chess Positions (2018) guided my selection of the seventh position (14-15).

White to move









14 November 2022

How bad is 2...Qf6?

Players relatively new to the game are often warned not to bring their queen out too early The move 2...Qf6 after 1.e4 e5 2.Nf3 was examined early in chess history. It appears in several manuscripts that reflect the work of Giulio Cesare Polerio and Gioachino Greco, and also in a sixteenth century manuscript reflecting the work of Pedro Damiano and Luis Ramirez de Lucena.

White to move
What should White do? I was surprised that my database of online games contains only 65 games with this position as it seems that I see it often lately. My score of 66% wins with White is unpleasant, too. I should have more success, especially as this queen foray is more often played by lower rated players. In fact, I underperform against it with a performance rating more than 100 lower that my average rating. My database also shows that I played this move once. I won with Black.

In the vast majority of the 304 games in ChessBase Mega 2020 that reached this position, White opts for one of two natural developing moves: 3.Nc3 is most popular (133 games), and second most often played is 3.Bc4 (93 games). Both score approximately 75%. I have played both of these moves and several others.

Monday morning, I opted for 3.c3, which I had played at least seven times prior. Although appearing in only five games in CB Mega, it may be the oldest response. It appears in the sixteenth century German MS produced by an unknown author sometime after 1512, purporting to present the work of Damiano and Lucena. Peter J. Monté has a chapter devoted to this MS in The Classical Era of Modern Chess (2014) and offers two lines after 3.c3 in Part II.

My game continued:

3...Bc5 4.d4 exd4

The German MS has 4...Bb6 and then 5.Be3 (5.h3 h6 6.Nxe5 d6 7.Nf3) 5...d6 6.dxe5 dxe5 7.Bg5 Qg6 8.Qd8#.

Three games on Lichess went as far as 6...dxe5 and then all had 7.Bxb6. After 7.Bg5, Black must play 7...Qd6, of course. 5.Be3 is not the strongest move in this old line. 5.a4, 5.Nxe5, and 5.dxe3 all give White a decisive advantage.

White to move
5.e5

If Black brings out the queen early, I should kick it around.

5.cxd4 is preferred by Stockfish. 5...Bb4+ 6.Nc3. White has a clear lead in development.

Perhaps White should favor normal development. What principles guide the punishment of Black's early queen foray?

5...Qg6

Although the engine favor removing the queen to its starting square, such a move is not in the spirit of 2...Qf6.

6.cxd4

Stockfish would give up prospects of castling kingside with 6.Bd3! Qxg2 7.Rg1 Qh3 8.Rg3 Qe6 9.cxd4 with a decisive advantage in the judgement of the software.

6...Bb4+ 7.Nc3

White has a comfortable position. A couple of moves later, my opponent gave up the dark-squared bishop for the gain of a pawn. I went on to win. My play was sloppy, failing to find the strongest moves. My reluctance to give up the g-pawn for an opportunity to chase Black's queen with developing moves is one lesson I take from this game.

The Doazan manuscript credited to Polerio offers two main lines that follow from 2...Qf6 (see "Classic Bishop Sacrifice: Early History" for a discussion of this MS). One of these lines leads to a clear advantage for White, but the other is less clear.

Polerio,Giulio Cesare [C40]
Doazan MS, c.1610

1.e4 e5 2.Nf3 Qf6 3.Nc3 Bc5

White to move
3...Bc5 is a terrible move that allows White to exploit the position of the Black queen. Polerio offers an instructive line that is worth learning.

4.Nd5 Qd6 or Qg6 5.d4 Bxd4 6.Nxd4 exd4 7.Bf4 1-0

Polerio,Giulio Cesare [C40]
Doazan MS, c. 1610

1.e4 e5 2.Nf3 Qf6 3.Nc3 c6

This move is much better that 3...Bc5.

4.Bc4 Bc5 5.0-0 d6

White to move
White is better, but Polerio's line does not demonstrate an advantage.

6.h3

6.d4 is suggested by Stockfish with a clear advantage for White.

6...Be6 7.Bb3 Nd7 8.d3 h6 9.Kh1 Ne7 10.Ng1 0-0 11.f4 

Polerio's line ends here. The position seems close to equal.

Gioachino Greco's explorations of this queen foray appear in the Paris (1625) and Orléans (n.d.) manuscripts. Monté notes that Orléans was likely copied from the Paris MS (339). ChessBase has three games from these explorations, although the lines given in that database are not entirely attested by Monté's compilation of lines found in sixteenth and seventeenth century manuscripts. I plan another post showing what we can know of Greco's work on 2...Qf6. (edit: now posted at "Greco on 2...Qf6")


11 November 2022

Desperation

Game 4 in Chess Informant 153 features a nice combination that I've enjoyed showing people the past few days. Black has a credible checkmate threat, so white cannot wait. From Martin Carmona--Kochmar, chess.com 2022.

White to move
What would you play? How deep can you see?

The annotator, Sasa Velickovic, gave three double-exclams to the winning combination.

09 November 2022

The Difference

Young players who wish to participate in the Washington State Elementary Chess Championships must qualify. They need to score 3.0 out of 5.0 possible in a qualifying event. I ran one of these qualifying events last Saturday. It was small so elementary students were playing in the same section as middle school and high school, making qualifying for elementary state more difficult. Nonetheless, two students succeeded!

Both of those elementary students who finished with 3.0 checkmated an opponent while I was watching their game. A young girl under immense pressure as the clock neared zero showed her mastery of the elementary checkmate with king and rook against king, although there were several other pieces on the board. When she slid her rook over to the a-file for checkmate, she had four second left.

A sixth grade boy provoked a confused look from his opponent as he appeared to have blundered his queen.

Black to move
After looking at him in confusion and looking at the queen, his opponent shrugged her shoulders and took the bait, 19...Qxf7. He answered quickly with 20.Rd8#.

In contrast, some of the players who finished with 2.5 points had a game where overwhelming force led only to a draw. In at least two cases, a player with two queens managed to leave their opponent no legal moves when not in check.

Black to move
White also had two bishops and a knight, but I do not recall the placement of all of them. Watching this particular game, I noticed that White systematically drove the lone king to the edge without checks, a vital skill when a single queen and king battle a lone king. With two queens, however, and other pieces on the board, the safest course is to deliver check every move.

My after school students this week see the checkmate trap set by one of their own, and they complete worksheets with mate in two. Last week, they did the mates in one.

This problem proves difficult for young players. From Bledow--Schorn, Berlin 1839.

White to move
This exercise is part of Rook Checkmates 4. RC 1 and 2 are mates in one. RC 3 and 4 are mates in two. 



06 November 2022

Knowing and Doing

My opponent's draw offer leads me to believe that he understood that a queen vs. a c-pawn one square from promotion is a draw. Nonetheless, I demanded proof and the opportunity to present it was missed. Alas, my own errors allowed the draw to remain after my opponent's first error, and the queen vs. pawn occurred only because I exchanged rooks when they should have remained on the board.

My individual students saw this endgame last week and then most of them solved some exercises from Georges Renaud and Victor Kahn, The Art of the Checkmate (1953). My afterschool club solved worksheets with checkmate in one. This week, they will see mates in two from some of the same games.

Black to move
56...Rxf6??

Simple counting shows that the next diagram will be reached. I should have played 56...Rc4.

57.Kxf6= Kf4 58.Ke7 g3 59.Kxd7 g2 60.c6 g1Q 61.c7 Qa7

White to move
62.Kd8??

Now, we have reached a position that I know from endgame books. 62.Kc6 was the only move to hold the draw.

62...Qb6??

I know, but did not do. After 62...Ke5-+ 63.c8Q Kd6, White is in zugzwang with a worthless king. In fact, Black has a mate in three.

63.Kd7= Qb5+ 64.Kd8 Qd5+ 65.Kc8 Ke5 66.Kb8 Qb5+ 67.Ka7 Qc6 67.Ka7 Qc6 68.Kb8 Qb6+

White to move
69.Kc8??

69.Ka8=. Knowing this stalemate resource is essential to understanding why a c- or f-pawn against the queen is a draw when the pawn is one square from promotion.

69...Kd6-+

White resigned.



30 October 2022

A Few Strong Moves

Playing ten minute Arena on Chess.com, I often play terrible chess. But, sometimes I play okay, too. This weekend, I won a couple of games with some strong moves. I also drew one with a nice combination.

This position arose from a Stafford Gambit. It often surprises me when a player rated over 1700 thinks they can castle.

Black to move
Nxf2!

Best move.

8...Bxf2+ 9.Rxf2 Qxf2+ 10.Kh1 h5 is also winning.

9.Qf3 moves into forced mate.

9.Rxf2 Qxf2+ 10.Kh1 Be6-+

9...Nxh3+ 10.Kh2 Ng5+

10...Nf2+ was better. 11.Qh3 Bd6+ 12.e5 Bxe5+ 13.Kg1 Nxh3+ 14.gxh3 Qg3+ 15.Kh1 Qh2#

11.Qh3 Bd6+ 12.Kg1

12.Kh1 resists longer. 12...Nxh3 13.Rf3 Ng5+ 14.Kg1 Nxf3+ 15.gxf3 Bc5+ 16.d4 Bxd4+ 17.Be3 Bxe3+ 18.Kf1 Qf2#

12...Nxh3+ 13.gxh3 Qg3+ 14.Kh1 Qh2# 0-1

This game went back and forth and the engine thinks I should have taken White's c-pawn at one point.

Black to move
36...Qf5+! 37.Ke2

White moves into a mate in four, which I found.
37.Kd2 was necessary, and I probably would not have found the best move: 37...Kc8!

37.Qc2+ 38.Kf1 Rh1+ 39.Kg2 Qg6+ 40.Kxh1 Rh8#

My best move today was one of several that led to equality, but was the only forcing move. White could have gone astray and lost.

Black to move
32...Nf4! 33.gxf4 Rg6+ 34.Kf1

After 34.Kh1 Qh3, White must force a draw by repetition.

34...Qh3+ 35.Ke1 Qc3+ 36.Rd2 Rg1+ 37.Bf1 Qc1+ 38.Rd1 Rxf1+ 39.Kxf1 Qxd1+ 40.Kg2 Qg4+ 41.Kf1 Qd1+ 42.Kg2 Game drawn by agreement ½-½



28 October 2022

Problem of the Week

Elementary checkmates

Several years ago, I developed the habit of posting a portion of each week's chess lessons for youth players on Chess Skills. These were labeled with "Problem of the Week". After a few years, I stopped doing these posts weekly, but would post one from time to time. I seem to be slipping back towards the regular habit.

My students this week in the after school club were presented with some checkmate positions.

On Tuesday I presented the first ten moves of a game that I played online the day prior, then asked students to work out the forced checkmate in five. Although the position differs slightly, the five move sequence is identical to one found in Vladimir Vukovic, The Art of Attack in Chess (1965).

Stripes,J. -- Internet Opponent [C10]
Live Chess Chess.com, 17.10.2022

1.e4 e6 2.d4 d5 3.Nc3 dxe4 4.Nxe4 Nf6 5.Bd3 Nxe4

5...Nbd7 has been my choice with Black.

6.Bxe4 Bd6

Both 6...c5 and 6...Nd7 are better.

7.Nf3 0-0 8.Bxh7+?

In this instance, the classic bishop sacrifice leads only to equality with best play.

8...Kxh7 9.Ng5+
Black to move
9...Kg8??

9...Kg6 was necessary 10.h4 Kf6 is best 11.Nh7+ Ke7 12.Nxf8 Kxf8 is best with equality.

10.Qh5+- Re8

Moves into forced checkmate

Black's woes are illustrated by the computer's suggested alternatives:
10...Bb4+ 11.c3; or
10...Qxg5 11.Bxg5

White to move

On Thursday, I first presented a situation that led to a draw in the previous Saturday's youth tournament. After more than a dozen moves, a young player with rook and knight against a lone king admitted inability to force checkmate. I asked a few students to show how they would find checkmate from this position.

White to move
After students showed their methods, I reviewed the process of keeping the Black king in an ever shrinking box. Then I presented a common exercise that Bruce Pandolfini has in his Pandolfini's Endgame Course (1988), 27.

White to move
Any rook move begins the process of delivering checkmate by force in three moves.

White has a mate in three with the rook on any square marked in yellow.

The real challenge was in solving a puzzle that dates from the mid-fifteenth century (before the bishop and queen gained the power they have now). 
White to move
Checkmate must be delivered in 12 moves or less. The rook can only move once was a stipulation of the problem. This problem shows that chess players know how to use opposition and outflanking more than 570 ago.