Detects an undefended square on the back rank (1st for white, 8th for black) that is attacked by exactly one white piece and exactly one black piece.

By Climbchess Research · 2026-05-08 · 3 min read · Updated May 8, 2026

SAE concept sae_12410 fires when detects an undefended square on the back rank (1st for white, 8th for black) that is attacked by exactly one white piece and exactly one black piece.. It appears in 1 of 9,950 Climbchess puzzles (0.0%), spanning ELO 849–849 (median 849).

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This page documents Detects an undefended square on the back rank…, one of 4,505 interpretable chess concepts extracted from Leela Chess Zero via sparse autoencoders. The full feature description from our SAE labelling pipeline reads:

Detects an undefended square on the back rank (1st for white, 8th for black) that is attacked by exactly one white piece and exactly one black piece.

This pattern fires in 1 of our 9,950 tagged puzzles. The puzzles where it appears span ELO 849 to 849, with a median rating of 849. That distribution tells you whether this is a beginner cue or a master-level subtlety.

Pattern statistics

Related concepts

The five concepts most often co-firing alongside this one (Jaccard similarity over the puzzle co-occurrence graph) are:

• A queen in a dominant advanced position, typically near or on the opponent's… — similarity 0.002
• Black rook on an active central or kingside file (d8–h8 range), not… — similarity 0.002
• A queen on a contested square with White to move, under pressure from enemy… — similarity 0.002
• A king on the back rank exposed to at least one enemy attacker with no… — similarity 0.000
• This feature detects a white queen on a square where it is not attacked by… — similarity 0.000

Example puzzles

Below are 1 puzzles spanning the rating distribution. Each links to its own page with full move list and related concepts.

• Puzzle zze9h_M — ELO 849, themes: kingsideAttack, mate, mateIn1, side to move: White

How to use this page

If you want to train this pattern, open the Climbchess trainer and filter for puzzles tagged with this concept. The trainer surfaces them at the right difficulty for your current rating, and tracks how often you spot the cue versus miss it. You can also browse the related concepts above to see neighbouring ideas in feature space.

Climbchess concepts are not heuristics written by a human author. Each one corresponds to a single direction in the residual stream of Leela Chess Zero that activates on a specific board feature, then was labelled by reading the top-activating positions. This makes the catalogue exhaustive (every Leela-detectable pattern is in here somewhere) and falsifiable (you can replay our extraction).