What "explain every attack" costs in a game story

A. The move Akshat shared

The game Akshat linked in Slack: app.zappchess.com/r/Upb2GOYYN8, room 7d98f212, story scene opponent-mistake-1-punishment, story told to White. Only the move he asked about is here, not the rest of his game.

Akshat: "It doesnt explain why bishop cant be taken back, nor how the best move prevents the bishop from being taken"

The story shows one line of 1 ply. A reader who asks "what if they take back?", "what if they check?" and "why was the best move safe?" needs 5 branches and 14 plies for this one scene: 14× the shown line. Only 1 of these is non-obvious (the moved piece does not simply hang): 4 plies. Every line below was found by the engine, not written by hand.

1. The scene as the story tells it now

The mistake: 29...Be7 (position before it: show)

Their move (Be7) was a mistake. It costs them a bishop: net +3 for you. Let's see how. They can't get it back. You played it in the game.

The line the story shows (1 ply):

2. "But what if they ...?" Every reply the reader may ask about

Black has 31 legal replies after Bxe7. These are the ones a reader asks about: taking the piece back, and other captures and checks. Each needs its own answer.

Take the piece back (1, 4 plies)

• take-back30...Rxe7 then 31.Qd8+Kh732.Qxe7 non-obvious+6.54 plies

Other captures and checks (3, 8 plies)

• check30...Qg2+ then 31.Kxg2b6 obvious: hangs to Kxg2White mates in 93 plies
• check30...Qg1+ then 31.Rxg1Rxe7 obvious: hangs to Kxg1White mates in 63 plies
• check30...Qe4+ then 31.Qxe4 obvious: hangs to Qxe4White mates in 102 plies

3. "How would the best move have prevented it?"

Instead of Be7, the best move was b6. To show that it is safe, the story must answer every capture and check White can try after it: 1 attack, 2 plies.

• 30.Qxf7+ then 30...Qxf7 obvious: hangs to Kxf7−9.22 plies

4. Totals for this one scene

B. The worst real case

Real ZappChess game, room 84eaab65-3878-44c5-961c-8084ba58670c, story scene opponent-mistake-1-punishment, story told to White. Worst case by ratio (full answer ÷ shown line) among the 740 scenes of the 146 fixture games. Scenes with bigger raw totals (up to 112 plies at depth 13) were already-lost positions, or their story claim did not survive a depth-20 check. This scene holds up at depth 20 (and at depth 22 for the take-backs).

The story shows one line of 1 ply. A reader who asks "what if they take back?", "what if they check?" and "why was the best move safe?" needs 11 branches and 60 plies for this one scene: 60× the shown line. Only 3 of these are non-obvious (the moved piece does not simply hang): 26 plies. Every line below was found by the engine, not written by hand.

1. The scene as the story tells it now

The mistake: 30...Rd5 (position before it: show)

Their move (Rd5) was a mistake. It costs them a rook: net +5 for you. Let's see how. They can't get it back. In the game you played (Re4), so you missed this chance.

The line the story shows (1 ply):

2. "But what if they ...?" Every reply the reader may ask about

Black has 26 legal replies after Rxd5. These are the ones a reader asks about: taking the piece back, and other captures and checks. Each needs its own answer.

Take the piece back (2, 17 plies)

• take-back31...exd5 then 32.Qxh6Qc233.c6Qc534.Qxg5+Kh735.Qf6Qa7 … the line goes on; the gain comes later non-obvious+10.69+ plies
• take-back31...Qxd5 then 32.c6Kh733.c7Qd734.Qb8Kg635.c8=Q non-obvious+10.48 plies

Other captures and checks (4, 16 plies)

• check31...Qxf3+ then 32.Kxf3exd533.Qxh6 obvious: hangs to Kxf3White mates in 224 plies
• check31...Qf1+ then 32.Kxf1exd533.Qxh6 obvious: hangs to Kxf1White mates in 374 plies
• check31...Qg1+ then 32.Kxg1exd533.Qxh6 obvious: hangs to Kxg1White mates in 534 plies
• check31...Qh1+ then 32.Kxh1exd533.Qxh6 obvious: hangs to Kxh1+88.04 plies

3. "How would the best move have prevented it?"

Instead of Rd5, the best move was Rd3. To show that it is safe, the story must answer every capture and check White can try after it: 5 attacks, 27 plies.

• 31.Qb8+ then 31...Kh732.Qb7Kg633.h4Kf634.hxg5+hxg535.Qe4 … the line goes on; the gain comes later non-obvious−0.19+ plies
• 31.Qd8+ then 31...Rxd8 obvious: hangs to Rxd8−10.22 plies
• 31.Qxe6 then 31...Qxf3+32.Kg1fxe633.Re1Rd234.Rf1Qxh3 obvious: hangs to fxe6Black mates in 108 plies
• 31.Rxe6 then 31...Qxf3+32.Kg1Rd1+33.Re1Rxe1+ obvious: hangs to fxe6Black mates in 46 plies
• 31.Rxg5+ then 31...hxg5 obvious: hangs to hxg5−5.62 plies

4. Totals for this one scene

C. A typical case: 3 non-obvious lines

Real ZappChess game, room 43beac72-d7a0-4217-ba6d-41ddcf9189fa, story scene opponent-mistake-2-punishment, story told to White. Picked from the 225 scenes (30% of 741) whose full answer has two or three non-obvious lines. At depth 13, the sweep depth, this scene needs 10 non-obvious plies: the middle value of that group. The lines below are depth 20. At depth 20 the engine gives a longer answer to Qxa7, and that line does not settle within the 8 plies the engine shows, so the count here is 19 plies with one line open.

The story shows one line of 1 ply. A reader who asks "what if they take back?", "what if they check?" and "why was the best move safe?" needs 12 branches and 65 plies for this one scene: 65× the shown line. Only 3 of these are non-obvious (the moved piece does not simply hang): 19 plies. Every line below was found by the engine, not written by hand.

1. The scene as the story tells it now

The mistake: 32...Re2+ (position before it: show)

Their move (Re2+) was a mistake. It costs them a rook: net +5 for you. Let's see how. They can't get it back. If they take with (Nxe2), (gxh5) wins their queen. In the game you played (Kf1), so you missed this chance.

The line the story shows (1 ply):

2. "But what if they ...?" Every reply the reader may ask about

Black has 32 legal replies after Nxe2. These are the ones a reader asks about: taking the piece back, and other captures and checks. Each needs its own answer.

Take the piece back (1, 4 plies)

• take-back33...Nxe2 then 34.gxh5h635.Qe8+ non-obviousWhite mates in 104 plies

Other captures and checks (5, 26 plies)

• capture33...Bxa3 then 34.gxh5h635.Qe8+ obvious: hangs to bxa3White mates in 74 plies
• check33...Qh3+ then 34.Kxh3h535.Qe8+ obvious: hangs to Kxh3White mates in 94 plies
• check33...Qxh2+ then 34.Kxh2Nf3+35.Rxf3 obvious: hangs to Kxh2White mates in 164 plies
• check33...Qxg4+ then 34.Rxg4b535.Qa6h536.Rg5Kg837.Qc8+ obvious: hangs to Rxg4White mates in 108 plies
• check33...Qd5+ then 34.Kh3g535.Rxd4Bxd436.Qxd4+ non-obvious+5.96 plies

3. "How would the best move have prevented it?"

Instead of Re2+, the best move was Qg6. To show that it is safe, the story must answer every capture and check White can try after it: 6 attacks, 35 plies.

• 33.Qxa7 then 33...Qc6+34.Kg3Qh135.Ne5Qg1+36.Kh3Qe3+37.Kg2 … the line goes on; the gain comes later non-obvious−9.89+ plies
• 33.Qxe8+ then 33...Qxe8 obvious: hangs to Qxe8−5.22 plies
• 33.Qxd4 then 33...Bxd434.Rxd4 obvious: hangs to Bxd4−5.53 plies
• 33.Rf8+ then 33...Rxf834.Nf2 obvious: hangs to Bxf8Black mates in 183 plies
• 33.Rxd4 then 33...b534.Ne5Qe635.Nxb5Qxe536.Rd2Rf837.Qc4 … the line goes on; the gain comes later obvious: hangs to Bxd4−4.39+ plies
• 33.Nxc5 then 33...bxc534.Qd7h635.h3Re536.Qb7Kh737.Re4 … the line goes on; the gain comes later obvious: hangs to bxc5−0.39+ plies

4. Totals for this one scene

Answer lines are cut as short as the engine allows: a reply's line stops at mate, or as soon as the material the story promised is back on the board and the other side has no capture left that wins it back; an attack's line stops at mate, or as soon as the attacker has lost material on balance and has no such capture left. A line marked "goes on" has not settled within the engine line shown. Longer lines would only make the totals bigger.

Across 740 scenes of 146 real games (depth 13): the story line has a median of 4 plies; 1 scene in 6 needs a full answer of 5 times the shown line or more; proving the best move safe needs a median of 3 refuted attacks and 16 plies.