The Audit of Move Nine: 9...a5 in the Mar del Plata and an Undated Advertisement

Last week a chess opening product landed in my inbox. The subject was the King's Indian Defence, Mar del Plata variation, a recommendation of 9...a5 for Black, described as an “antidote” to the Bayonet Attack. I read it the way I read everything: first I count how many claims in the document can actually be verified. Nine information points. Not one complete move sequence, not one named game, no player, no author, no publisher, no price, no date, and not a single engine evaluation. The spreadsheet had twelve hundred rows and every row was a small confession; here there are nine rows and one confession — the claims exist, the numbers do not.

That contradiction is the most honest thing in the document, and it is why I read it as an audit rather than an opening review.

Context, for readers who do not keep the King's Indian calendar

The Classical Mar del Plata stem runs 1.d4 Nf6 2.c4 g6 3.Nc3 Bg7 4.e4 d6 5.Nf3 0-0 6.Be2 e5 7.0-0 Nc6 8.d5 Ne7. Two pawn walls face each other — White's on the queenside, Black's on the kingside. On move nine, White's 9.b4 is the Bayonet Attack: a queenside clamp with b4-b5 and c4-c5 behind it. Black's main reply for decades has been 9...Nh5, which drags the game into a channel of forcing moves and is therefore easy to check with an engine. The 9...a5 the advertisement promotes strikes at the root of that clamp — an attempt to settle the queenside account first, then fight a manoeuvring battle.

The Bayonet is no fashion. Players of Kramnik's generation brought it back into elite practice in the 1990s, and it has been a standing problem for Black ever since — that is my external knowledge, not the source's claim. The source only calls it “fashionable,” and that word choice is the first sign that the advertisement is selling an old problem as a new one.

The audit: five claims and the bill attached to each

The first claim the source concedes itself — “objectively the chances are equal.” That is unusual honesty for promotional copy, and it is also the loudest technical signal. 9...a5 is an equalising tool, not a refutation. For a Black player who needs a win in the last round, the utility of that tool is structurally limited, and that sentence does not appear in the product listing.

Second claim, the engine of the whole advertisement: “computers often do not know how to handle these complex strategic positions.” That sentence is written in the language of the 2000s and does not survive the neural-engine era as stated. The defensible version is narrower: in closed positions engine evaluations are less stable and less humanly actionable — numbers hovering near zero that are hard to convert into a plan. That is a statement about usability, not about engine ignorance. The advertisement blurs the two, deliberately.

Third claim — “very few concrete lines, strategy over tactics” — is internally consistent and commercially self-undermining. A low-forcing line cannot be tested by the buyer before purchase, because there is no forcing sequence to test; and it cannot be refuted afterwards either, because there is no route to refutation. In my reading this is the product's central weakness: the claim is unfalsifiable. An unfalsifiable claim protects the author from criticism and drives away the sophisticated buyer.

Fourth, the actual chess argument, which I accept. 9.b4 is a claim on space; 9...a5 cuts at the root of that claim and steers the game away from the forcing 9...Nh5 channels into manoeuvring. It is a legitimate “avoid the machine, play the human” design — with a visible price: Black accepts a permanently smaller share of the position's dynamic assets in exchange for strategic clarity. That can be a good trade. It is not a free one.

Fifth, the word “fashionable.” A line that has sat in the mainstream for thirty years is being called a fashion for one purpose — to make an old problem look new so that a new solution can be priced.

The contrarian reading, and the boring number left out

The reflex is to say that a low-theory line is a weak line. I read it the other way: for this particular buyer the product may be better. A club player tired of engine-driven preparation wants the memorisation load reduced — and, conveniently, that same buyer will not demand engine numbers. The absence of data is not an accident; it is market segmentation. That is a coherent strategy, and it explains why the document contains not one evaluation.

But correlation and causation part company here. If 9...a5 works in practice, it will be the fruit of unfamiliarity, not of objective superiority. A line that deserved to sit as close to elite practice as 9...Nh5 would already be there. Low theoretical density usually means “playable and unrefuted,” not “strong.” And the boring number should be published too: the boring finding in this whole affair is that 9...a5 is playable. That is all it establishes. When the boring number is the finding, print the boring number.

My first on-site in Kolkata taught me that a stadium is also a ledger. I logged ninety rapid and blitz games there for clock use and engine swings, and the lesson was that form has to be separated from noise. Here the noise is the advertisement; the form is one move. I do not chase the story; I trace the paperwork until it speaks. In this paperwork there is exactly one line that speaks — 9...a5, with no date under it.

One human line belongs in this accounting, or the ledger becomes the story. Consider the 2026-rated club player who buys the product before a weekend Swiss, plays 9...a5 on Saturday morning, and by move eleven finds himself in a passive position with no forcing line to fall back on — because the product promised “very few concrete lines.” His loss will never be recorded, because the game will never be published.

What to watch next

The real test is not a review, it is a database. If in the next twelve months no player above 2400 plays this line two or three times in published classical games, the claim stays where it started — inside an undated advertisement. And if one does, look at why the win arrived: the opponent's unfamiliarity, or the position's genuine strength. My method is simple: watch, log, wait, and let the contradiction surface. The question is not whether 9...a5 is a good move. The question is how many study hours a “few concrete lines” product demands from its buyer — and which account those hours are billed to.