{"abstract":"A king cannot step from e4 to f5.","category":"Chess move legality","checks":8,"contract":"Input: {\"board\", \"from\": king square, \"to\": square}. Return true when the king move is legal: exactly one square in any direction, not onto a friendly piece, and the destination is not attacked by the opponent (including the enemy king) once the king has left its origin square. Captures of undefended enemy pieces are allowed.","contract_signature":"x","evaluation_group":"w2-chess_move_legality-king-step-safety","failed_approach":"Accepting a Manhattan distance of 1 or 2 also admits two-square straight moves such as e4-e6.","family":"w2-chess_move_legality-king-step-safety-step-distance","id":"FA-82471","implementations":{"attempt":{"sha256":"b9952108bfa5f64ce37c0b246324d49f98070a9447cb8055d91dd334d7f58edf","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x):\n    def attacked(bd, sq, by_white):\n        f,r=ord(sq[0])-97,int(sq[1])-1\n        def at(ff,rr):\n            return bd.get(chr(97+ff)+str(rr+1)) if 0<=ff<8 and 0<=rr<8 else None\n        P,N,B,R,Q,K=('PNBRQK' if by_white else 'pnbrqk')\n        pr=r-1 if by_white else r+1\n        if at(f-1,pr)==P or at(f+1,pr)==P: return True\n        for df,dr in ((1,2),(2,1),(-1,2),(-2,1),(1,-2),(2,-1),(-1,-2),(-2,-1)):\n            if at(f+df,r+dr)==N: return True\n        for df in (-1,0,1):\n            for dr in (-1,0,1):\n                if (df or dr) and at(f+df,r+dr)==K: return True\n        for df,dr,kinds in ((1,0,(R,Q)),(-1,0,(R,Q)),(0,1,(R,Q)),(0,-1,(R,Q)),(1,1,(B,Q)),(1,-1,(B,Q)),(-1,1,(B,Q)),(-1,-1,(B,Q))):\n            ff,rr=f+df,r+dr\n            while 0<=ff<8 and 0<=rr<8:\n                v=at(ff,rr)\n                if v:\n                    if v in kinds: return True\n                    break\n                ff+=df; rr+=dr\n        return False\n    \n    b=x['board']; fr,to=x['from'],x['to']; k=b[fr]; white=k=='K'\n    df=ord(to[0])-ord(fr[0]); dr=int(to[1])-int(fr[1])\n    if abs(df)+abs(dr) not in (1,2): return False\n    occ=b.get(to)\n    if occ and occ.isupper()==white: return False\n    nb=dict(b); del nb[fr]; nb[to]=k\n    return not attacked(nb, to, not white)\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nfixtures = [[('retreat along rook file',\n   {'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),\n  ('sidestep rook file', {'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'd3'},\n   True),\n  ('diagonal step', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'f5'}, True),\n  ('stand still', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e4'}, False),\n  ('capture own', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'P'}, 'from': 'e4', 'to': 'e5'}, False),\n  ('capture undefended', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'p'}, 'from': 'e4', 'to': 'e5'},\n   True),\n  ('capture defended',\n   {'board': {'a8': 'k', 'd6': 'p', 'e4': 'K', 'e5': 'p'}, 'from': 'e4', 'to': 'e5'}, False),\n  ('two squares', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e6'}, False)],\n [('diagonal step', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'f5'}, True),\n  ('capture undefended', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'p'}, 'from': 'e4', 'to': 'e5'},\n   True),\n  ('capture defended',\n   {'board': {'a8': 'k', 'd6': 'p', 'e4': 'K', 'e5': 'p'}, 'from': 'e4', 'to': 'e5'}, False),\n  ('next to enemy king orthogonal', {'board': {'e4': 'K', 'e6': 'k'}, 'from': 'e4', 'to': 'e5'},\n   False),\n  ('next to enemy king diagonal', {'board': {'e4': 'K', 'g6': 'k'}, 'from': 'e4', 'to': 'f5'},\n   False),\n  ('knight below', {'board': {'a8': 'k', 'e4': 'K', 'f1': 'n'}, 'from': 'e4', 'to': 'e3'}, False),\n  ('two squares', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e6'}, False),\n  ('knight far below', {'board': {'a8': 'k', 'c4': 'n', 'e4': 'K'}, 'from': 'e4', 'to': 'd3'},\n   True)],\n [('sidestep rook file', {'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'd3'},\n   True),\n  ('next to enemy king diagonal', {'board': {'e4': 'K', 'g6': 'k'}, 'from': 'e4', 'to': 'f5'},\n   False),\n  ('knight below', {'board': {'a8': 'k', 'e4': 'K', 'f1': 'n'}, 'from': 'e4', 'to': 'e3'}, False),\n  ('knight above', {'board': {'a8': 'k', 'd7': 'n', 'e4': 'K'}, 'from': 'e4', 'to': 'e5'}, False),\n  ('black king bishop diag retreat',\n   {'board': {'b3': 'B', 'd5': 'k', 'h1': 'K'}, 'from': 'd5', 'to': 'e6'}, False),\n  ('capture along check line',\n   {'board': {'a1': 'k', 'e3': 'p', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),\n  ('two squares', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e6'}, False),\n  ('knight far below', {'board': {'a8': 'k', 'c4': 'n', 'e4': 'K'}, 'from': 'e4', 'to': 'd3'},\n   True)],\n [('retreat along rook file',\n   {'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),\n  ('sidestep rook file', {'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'd3'},\n   True),\n  ('diagonal step', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'f5'}, True),\n  ('black king bishop diag retreat',\n   {'board': {'b3': 'B', 'd5': 'k', 'h1': 'K'}, 'from': 'd5', 'to': 'e6'}, False),\n  ('capture along check line',\n   {'board': {'a1': 'k', 'e3': 'p', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),\n  ('capture defended knight',\n   {'board': {'a8': 'k', 'e4': 'K', 'e5': 'n', 'e7': 'r'}, 'from': 'e4', 'to': 'e5'}, False),\n  ('two squares', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e6'}, False),\n  ('knight far below', {'board': {'a8': 'k', 'c4': 'n', 'e4': 'K'}, 'from': 'e4', 'to': 'd3'},\n   True)],\n [('retreat along rook file',\n   {'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),\n  ('sidestep rook file', {'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'd3'},\n   True),\n  ('diagonal step', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'f5'}, True),\n  ('stand still', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e4'}, False),\n  ('capture own', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'P'}, 'from': 'e4', 'to': 'e5'}, False),\n  ('capture undefended', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'p'}, 'from': 'e4', 'to': 'e5'},\n   True),\n  ('two squares', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e6'}, False),\n  ('knight far below', {'board': {'a8': 'k', 'c4': 'n', 'e4': 'K'}, 'from': 'e4', 'to': 'd3'},\n   True)]]\nfor label, args, expected in fixtures[N-1]:\n    try:\n        actual = solve(args)\n    except Exception as exc:\n        actual = 'error:' + type(exc).__name__\n    check(label, actual, expected)\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"},"broken":{"sha256":"89672ce17fbdcbf28c927627f94b4b538966f609114dc4d304ec072650972661","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x):\n    def attacked(bd, sq, by_white):\n        f,r=ord(sq[0])-97,int(sq[1])-1\n        def at(ff,rr):\n            return bd.get(chr(97+ff)+str(rr+1)) if 0<=ff<8 and 0<=rr<8 else None\n        P,N,B,R,Q,K=('PNBRQK' if by_white else 'pnbrqk')\n        pr=r-1 if by_white else r+1\n        if at(f-1,pr)==P or at(f+1,pr)==P: return True\n        for df,dr in ((1,2),(2,1),(-1,2),(-2,1),(1,-2),(2,-1),(-1,-2),(-2,-1)):\n            if at(f+df,r+dr)==N: return True\n        for df in (-1,0,1):\n            for dr in (-1,0,1):\n                if (df or dr) and at(f+df,r+dr)==K: return True\n        for df,dr,kinds in ((1,0,(R,Q)),(-1,0,(R,Q)),(0,1,(R,Q)),(0,-1,(R,Q)),(1,1,(B,Q)),(1,-1,(B,Q)),(-1,1,(B,Q)),(-1,-1,(B,Q))):\n            ff,rr=f+df,r+dr\n            while 0<=ff<8 and 0<=rr<8:\n                v=at(ff,rr)\n                if v:\n                    if v in kinds: return True\n                    break\n                ff+=df; rr+=dr\n        return False\n    \n    b=x['board']; fr,to=x['from'],x['to']; k=b[fr]; white=k=='K'\n    df=ord(to[0])-ord(fr[0]); dr=int(to[1])-int(fr[1])\n    if abs(df)+abs(dr)!=1: return False\n    occ=b.get(to)\n    if occ and occ.isupper()==white: return False\n    nb=dict(b); del nb[fr]; nb[to]=k\n    return not attacked(nb, to, not white)\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nfixtures = [[('retreat along rook file',\n   {'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),\n  ('sidestep rook file', {'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'd3'},\n   True),\n  ('diagonal step', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'f5'}, True),\n  ('stand still', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e4'}, False),\n  ('capture own', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'P'}, 'from': 'e4', 'to': 'e5'}, False),\n  ('capture undefended', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'p'}, 'from': 'e4', 'to': 'e5'},\n   True),\n  ('capture defended',\n   {'board': {'a8': 'k', 'd6': 'p', 'e4': 'K', 'e5': 'p'}, 'from': 'e4', 'to': 'e5'}, False),\n  ('two squares', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e6'}, False)],\n [('diagonal step', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'f5'}, True),\n  ('capture undefended', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'p'}, 'from': 'e4', 'to': 'e5'},\n   True),\n  ('capture defended',\n   {'board': {'a8': 'k', 'd6': 'p', 'e4': 'K', 'e5': 'p'}, 'from': 'e4', 'to': 'e5'}, False),\n  ('next to enemy king orthogonal', {'board': {'e4': 'K', 'e6': 'k'}, 'from': 'e4', 'to': 'e5'},\n   False),\n  ('next to enemy king diagonal', {'board': {'e4': 'K', 'g6': 'k'}, 'from': 'e4', 'to': 'f5'},\n   False),\n  ('knight below', {'board': {'a8': 'k', 'e4': 'K', 'f1': 'n'}, 'from': 'e4', 'to': 'e3'}, False),\n  ('two squares', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e6'}, False),\n  ('knight far below', {'board': {'a8': 'k', 'c4': 'n', 'e4': 'K'}, 'from': 'e4', 'to': 'd3'},\n   True)],\n [('sidestep rook file', {'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'd3'},\n   True),\n  ('next to enemy king diagonal', {'board': {'e4': 'K', 'g6': 'k'}, 'from': 'e4', 'to': 'f5'},\n   False),\n  ('knight below', {'board': {'a8': 'k', 'e4': 'K', 'f1': 'n'}, 'from': 'e4', 'to': 'e3'}, False),\n  ('knight above', {'board': {'a8': 'k', 'd7': 'n', 'e4': 'K'}, 'from': 'e4', 'to': 'e5'}, False),\n  ('black king bishop diag retreat',\n   {'board': {'b3': 'B', 'd5': 'k', 'h1': 'K'}, 'from': 'd5', 'to': 'e6'}, False),\n  ('capture along check line',\n   {'board': {'a1': 'k', 'e3': 'p', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),\n  ('two squares', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e6'}, False),\n  ('knight far below', {'board': {'a8': 'k', 'c4': 'n', 'e4': 'K'}, 'from': 'e4', 'to': 'd3'},\n   True)],\n [('retreat along rook file',\n   {'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),\n  ('sidestep rook file', {'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'd3'},\n   True),\n  ('diagonal step', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'f5'}, True),\n  ('black king bishop diag retreat',\n   {'board': {'b3': 'B', 'd5': 'k', 'h1': 'K'}, 'from': 'd5', 'to': 'e6'}, False),\n  ('capture along check line',\n   {'board': {'a1': 'k', 'e3': 'p', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),\n  ('capture defended knight',\n   {'board': {'a8': 'k', 'e4': 'K', 'e5': 'n', 'e7': 'r'}, 'from': 'e4', 'to': 'e5'}, False),\n  ('two squares', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e6'}, False),\n  ('knight far below', {'board': {'a8': 'k', 'c4': 'n', 'e4': 'K'}, 'from': 'e4', 'to': 'd3'},\n   True)],\n [('retreat along rook file',\n   {'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),\n  ('sidestep rook file', {'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'd3'},\n   True),\n  ('diagonal step', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'f5'}, True),\n  ('stand still', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e4'}, False),\n  ('capture own', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'P'}, 'from': 'e4', 'to': 'e5'}, False),\n  ('capture undefended', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'p'}, 'from': 'e4', 'to': 'e5'},\n   True),\n  ('two squares', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e6'}, False),\n  ('knight far below', {'board': {'a8': 'k', 'c4': 'n', 'e4': 'K'}, 'from': 'e4', 'to': 'd3'},\n   True)]]\nfor label, args, expected in fixtures[N-1]:\n    try:\n        actual = solve(args)\n    except Exception as exc:\n        actual = 'error:' + type(exc).__name__\n    check(label, actual, expected)\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"}},"limitations":"A deterministic toy model with an explicitly stated contract; boards are {square: piece} with white upper-case and black lower-case pieces; no claim of full FIDE Laws conformance. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.","method":"Deterministic executable model with adversarial boundary fixtures.","provenance":{"created_by":"Failure Map","dependencies":"Python standard library","family":"w2-chess_move_legality-king-step-safety-step-distance","generated_at":"2026-09-29T14:50:12.502761+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"Move validators gate every move in engines, servers and arbiters; accepting an illegal move or rejecting a legal one corrupts the game record.","root_cause":"The step test uses Manhattan distance 1, which excludes diagonal moves.","sha256":"3c9f777ac0369d62e6f613f213a872c14fbbaafa9436bf88e83919248e124b1c","title":"King denied diagonal steps · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":39.301,"exit_code":1,"observations":[{"actual":false,"check":"retreat along rook file","expected":false,"passed":true},{"actual":true,"check":"sidestep rook file","expected":true,"passed":true},{"actual":true,"check":"diagonal step","expected":true,"passed":true},{"actual":false,"check":"stand still","expected":false,"passed":true},{"actual":false,"check":"capture own","expected":false,"passed":true},{"actual":true,"check":"capture undefended","expected":true,"passed":true},{"actual":false,"check":"capture defended","expected":false,"passed":true},{"actual":true,"check":"two squares","expected":false,"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"retreat along rook file\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"sidestep rook file\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"diagonal step\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"stand still\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"capture own\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"capture undefended\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"capture defended\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"two squares\", \"actual\": true, \"expected\": false, \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":41.647,"exit_code":1,"observations":[{"actual":false,"check":"retreat along rook file","expected":false,"passed":true},{"actual":false,"check":"sidestep rook file","expected":true,"passed":false},{"actual":false,"check":"diagonal step","expected":true,"passed":false},{"actual":false,"check":"stand still","expected":false,"passed":true},{"actual":false,"check":"capture own","expected":false,"passed":true},{"actual":true,"check":"capture undefended","expected":true,"passed":true},{"actual":false,"check":"capture defended","expected":false,"passed":true},{"actual":false,"check":"two squares","expected":false,"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"retreat along rook file\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"sidestep rook file\", \"actual\": false, \"expected\": true, \"passed\": false}, {\"check\": \"diagonal step\", \"actual\": false, \"expected\": true, \"passed\": false}, {\"check\": \"stand still\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"capture own\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"capture undefended\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"capture defended\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"two squares\", \"actual\": false, \"expected\": false, \"passed\": true}], \"passed\": false}\n"}},"member_only":{"stages":["fixed"],"fields":["implementations.fixed","verification.fixed","harness","repair"],"note":"The verified repair, its recorded checks, the repair description, and the scoring harness are available to members."}}