9
While I don't disagree with the spirit of Wes' answer, I want to answer your question in a somewhat stronger way, one that I think goes further toward relieving any possible confusion about this issue. Your question is:
Can a set of moves be a transposition and a variation?
My answer would be that neither transpositions nor variations should be thought ...
8
In one sense, I would simply say, "Yes, the pawn structure would be the first indicator that one has entered/transposed into a given opening." But since there's no other answer here as of yet, I'm going to take the liberty to say a bit more, pushing a little further than the question as you asked it.
Not to put too fine a point on it, but here's one way to ...
7
A transposition usually has to do with openings. Basically, it's all about move order, so while you might say that this is the modern defense (A40):
1. e4 g6 2. d4 Bg7 3. Nf3
If black follows with:
3. ... c5
It effectively transposes the opening into one of the Sicilian lines (B27):
1.e4 c5 2.Nf3 g6 3.d4 Bg7
Note that both positions are the same, only ...
7
You need to realize that just because someone gave it that name on move two, that it is certainly going to transpose to another opening with a different name. When determining what opening is played, classification takes place from the end of the game, and moves backward so the last known opening position is considered the opening that was played. If you ...
6
After 5....b5 6.Bb3 Be7, white has the strong option to play 7.d4. Now, 7....exd4 is a mistake, as white obtains a big advantage after 8.e5 Ne4 9.Bd5, which was played in Grischuk-Nepomniachtchi (blitz). Instead, 7....d6 is more stubborn.
In contrast, after 5....Be7, 6.d4 is relatively harmless for black, for example 6....exd4 7.e5 Ne4 8.Re1 Nc5.
[...
6
If you don't take on d5, I think the only advantage black has gained is flexibility. That means he can choose his opening according to your move. But you can be almost 100% sure that the opening will be transposed into some traditional line so white can't be worse, for example:
Slav Defence:
[FEN ""]
1. d4 d5 2. c4 Nf6?! 3. Nc3 (3. Nf3 c6) c6 {with the ...
4
Another possible transposition after 3. Nc3:
After 1. d4 d5 2. c4 Nf6 3. Nc3 Nc6 we arrive at a variation of the Chigorin Defense.
A particularly tricky line is the following.
[FEN ""]
[Title "Chigorin Defense"]
[Startply "6"]
1. d4 d5 2. c4 Nf6 3. Nc3 Nc6 4. cxd5 Nxd5 5. e4 Nxc3 6. bxc3 e5
4
In Andrew Soltis' book Pawn Structure Chess, he goes into great detail on the types of pawn positions you run into with specific openings, how they relate to other openings with similar structures, and when the transpositions are common.
I'd look into that resource and others like it for the specifics you're searching for.
3
No. You shouldn't count null-move in repetitions because:
Null-move is fake
Null-move artificially creates a repetition when there is none
Your implementation is correct, but you might want to exclude null-move. Let's take a look at Stockfish:
https://github.com/official-stockfish/Stockfish/blob/master/src/position.cpp
bool Position::is_draw(int ply) ...
3
With both move orders white can avoid the Benoni. The difference is all about which sidelines you allow and which ones you don't.
1. Nf3 c5 2. c4 is generally considered the most flexible move order for white since they can wait and play d4 at the moment of their choosing.
1. d4 Nf6 2. c4 c5 3. Nf3 cxd4 4. Nxd4 on the other hand gives black extra options, ...
2
Can the Nc3+e3 Chebanenko Slav, the Exchange Slav and the 4…Bg4 Slow Slav transpose into each other?
No, they don't transpose to Exchange Slavs.
In the Slow Slav and the Chebanenko, white plays e3 to prevent trouble with the c4 pawn. The bishop stays inside the pawn chain which is somewhat passive, but the plus is that c4 is defended, so that black can't stir up trouble by taking it and defending it with ...b5.
In the Exchange, white has dealt with that ...
2
One transposition white can try is from the French Exchange variation (if you know your opponent plays the French).
[FEN ""]
1. e4 e6 2. d4 d5 3. exd5 exd5 4. c4 dxc4 (4... Nf6) 5. Bxc4
It transposes to the variation 1. d4 d5 2. c4 dxc4 3. e3 e5 4. Bxc4 exd4 5. exd4 from this question.
In the French move order, clever black players won't take the pawn on ...
2
EDIT: You seem to be concerned if the opening is "tournament tested." I can affirm that almost all of the mainstream openings are well-tested, and you can figure out what these are yourself by doing the appropriate research online (i.e, which openings are most commonly played. See the links I supplied with this post.)
It would be great if you could clarify ...
2
There are indeed a couple of transpositions from the Nimzo-Indian to the Panov variation of the Caro-Kann and they occur sometimes in practical games.
Using a database of chess games, they can be filtered by searching simultaneously on:
The position after 1.d4 Nf6 2.c4 e6 3.Nc3 Bb4
"B10-B19", i.e. the ECO-code of the Caro-Kann.
After finding the games ...
1
I've toyed with this idea in the past but never played it seriously. If you're okay with the transpositions there is nothing wrong with it at all.
After 1.e4, e6 2. d4, c5 white has three main choices (3. Bxc5 is obviously really bad for white)
Nf3, cxd4 transposes to an e6 Sicilian. There's nothing wrong with that
d5 is a Franco-Benoni. Black can end ...
1
Your question has two different nuances, that is, how to classify an opening and how to classify a game.
The Encyclopedia of Chess Openings' only aim is to classify the first moves of a chess game, it does not concern itself with how the game develops nor further transpositions. Even if a widely known position is reached after an unorthodox choice of moves, ...
1
Playing 2...Nf6 requires black's willingness to play 3.cxd5 c6 lines, because black really needs a pawn recapture on d5. If he is ok with that and is prepared schematically for the lines arising after white declines playing cxd5, then sure, why not. Chess, like life, sometimes does not have absolute answers, especially at sub-Master levels. It is more ...
1
The simple version, with no variations: With 1 Nf3 2 c4 White is basically declaring the desire not to play Benoni. And if Black decides to go for it willy-nilly, Black knows they will quite likely end up in various variations of the Queen's Indian, the QGD (probably Tarrasch) or the Sicilian, including many Maroczy Bind possibilities. So Black chooses ...
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