FA-82466 / Chess move legality / Open access
King retreats along the checking line · case 01
A king on e4 checked by a rook on e8 may step back to e3.
ROOT CAUSE
The safety test runs with the king still on its origin square, which shields the destination from the rook.
VERIFIED REPAIR
Remove the king from its origin and place it on the destination before testing attacks.
Unsuccessful approach: Vacating the origin only for quiet moves still lets a capturing king hide behind its own origin square.
Case 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.
Why this case matters
Move validators gate every move in engines, servers and arbiters; accepting an illegal move or rejecting a legal one corrupts the game record.
1 / The failure
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(x):
def attacked(bd, sq, by_white):
f,r=ord(sq[0])-97,int(sq[1])-1
def at(ff,rr):
return bd.get(chr(97+ff)+str(rr+1)) if 0<=ff<8 and 0<=rr<8 else None
P,N,B,R,Q,K=('PNBRQK' if by_white else 'pnbrqk')
pr=r-1 if by_white else r+1
if at(f-1,pr)==P or at(f+1,pr)==P: return True
for df,dr in ((1,2),(2,1),(-1,2),(-2,1),(1,-2),(2,-1),(-1,-2),(-2,-1)):
if at(f+df,r+dr)==N: return True
for df in (-1,0,1):
for dr in (-1,0,1):
if (df or dr) and at(f+df,r+dr)==K: return True
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))):
ff,rr=f+df,r+dr
while 0<=ff<8 and 0<=rr<8:
v=at(ff,rr)
if v:
if v in kinds: return True
break
ff+=df; rr+=dr
return False
b=x['board']; fr,to=x['from'],x['to']; k=b[fr]; white=k=='K'
df=ord(to[0])-ord(fr[0]); dr=int(to[1])-int(fr[1])
if max(abs(df),abs(dr))!=1: return False
occ=b.get(to)
if occ and occ.isupper()==white: return False
nb=dict(b); nb[to]=k
return not attacked(nb, to, not white)
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('retreat along rook file',
{'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),
('sidestep rook file', {'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'd3'},
True),
('diagonal step', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'f5'}, True),
('stand still', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e4'}, False),
('capture own', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'P'}, 'from': 'e4', 'to': 'e5'}, False),
('capture undefended', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'p'}, 'from': 'e4', 'to': 'e5'},
True),
('black king bishop diag retreat',
{'board': {'b3': 'B', 'd5': 'k', 'h1': 'K'}, 'from': 'd5', 'to': 'e6'}, False),
('capture along check line',
{'board': {'a1': 'k', 'e3': 'p', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False)],
[('capture own', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'P'}, 'from': 'e4', 'to': 'e5'}, False),
('capture undefended', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'p'}, 'from': 'e4', 'to': 'e5'},
True),
('capture defended',
{'board': {'a8': 'k', 'd6': 'p', 'e4': 'K', 'e5': 'p'}, 'from': 'e4', 'to': 'e5'}, False),
('next to enemy king orthogonal', {'board': {'e4': 'K', 'e6': 'k'}, 'from': 'e4', 'to': 'e5'},
False),
('next to enemy king diagonal', {'board': {'e4': 'K', 'g6': 'k'}, 'from': 'e4', 'to': 'f5'},
False),
('knight below', {'board': {'a8': 'k', 'e4': 'K', 'f1': 'n'}, 'from': 'e4', 'to': 'e3'}, False),
('black king bishop diag retreat',
{'board': {'b3': 'B', 'd5': 'k', 'h1': 'K'}, 'from': 'd5', 'to': 'e6'}, False),
('capture along check line',
{'board': {'a1': 'k', 'e3': 'p', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False)],
[('retreat along rook file',
{'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),
('next to enemy king orthogonal', {'board': {'e4': 'K', 'e6': 'k'}, 'from': 'e4', 'to': 'e5'},
False),
('next to enemy king diagonal', {'board': {'e4': 'K', 'g6': 'k'}, 'from': 'e4', 'to': 'f5'},
False),
('knight below', {'board': {'a8': 'k', 'e4': 'K', 'f1': 'n'}, 'from': 'e4', 'to': 'e3'}, False),
('knight above', {'board': {'a8': 'k', 'd7': 'n', 'e4': 'K'}, 'from': 'e4', 'to': 'e5'}, False),
('capture along check line',
{'board': {'a1': 'k', 'e3': 'p', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),
('capture defended knight',
{'board': {'a8': 'k', 'e4': 'K', 'e5': 'n', 'e7': 'r'}, 'from': 'e4', 'to': 'e5'}, False),
('two squares', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e6'}, False)],
[('retreat along rook file',
{'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),
('sidestep rook file', {'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'd3'},
True),
('knight above', {'board': {'a8': 'k', 'd7': 'n', 'e4': 'K'}, 'from': 'e4', 'to': 'e5'}, False),
('black king bishop diag retreat',
{'board': {'b3': 'B', 'd5': 'k', 'h1': 'K'}, 'from': 'd5', 'to': 'e6'}, False),
('capture along check line',
{'board': {'a1': 'k', 'e3': 'p', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),
('capture defended knight',
{'board': {'a8': 'k', 'e4': 'K', 'e5': 'n', 'e7': 'r'}, 'from': 'e4', 'to': 'e5'}, False),
('two squares', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e6'}, False),
('knight far below', {'board': {'a8': 'k', 'c4': 'n', 'e4': 'K'}, 'from': 'e4', 'to': 'd3'},
True)],
[('retreat along rook file',
{'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),
('sidestep rook file', {'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'd3'},
True),
('diagonal step', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'f5'}, True),
('stand still', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e4'}, False),
('capture own', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'P'}, 'from': 'e4', 'to': 'e5'}, False),
('black king bishop diag retreat',
{'board': {'b3': 'B', 'd5': 'k', 'h1': 'K'}, 'from': 'd5', 'to': 'e6'}, False),
('capture along check line',
{'board': {'a1': 'k', 'e3': 'p', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),
('knight far below', {'board': {'a8': 'k', 'c4': 'n', 'e4': 'K'}, 'from': 'e4', 'to': 'd3'},
True)]]
for label, args, expected in fixtures[N-1]:
try:
actual = solve(args)
except Exception as exc:
actual = 'error:' + type(exc).__name__
check(label, actual, expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| retreat along rook file | True | False | Failed |
| sidestep rook file | True | True | Passed |
| diagonal step | True | True | Passed |
| stand still | False | False | Passed |
| capture own | False | False | Passed |
| capture undefended | True | True | Passed |
| black king bishop diag retreat | True | False | Failed |
| capture along check line | True | False | Failed |
SHA-256 / 0c9f75c876648db809819589ca2bcb6a0a03a60e535ff42443c372ec18fccc53
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(x):
def attacked(bd, sq, by_white):
f,r=ord(sq[0])-97,int(sq[1])-1
def at(ff,rr):
return bd.get(chr(97+ff)+str(rr+1)) if 0<=ff<8 and 0<=rr<8 else None
P,N,B,R,Q,K=('PNBRQK' if by_white else 'pnbrqk')
pr=r-1 if by_white else r+1
if at(f-1,pr)==P or at(f+1,pr)==P: return True
for df,dr in ((1,2),(2,1),(-1,2),(-2,1),(1,-2),(2,-1),(-1,-2),(-2,-1)):
if at(f+df,r+dr)==N: return True
for df in (-1,0,1):
for dr in (-1,0,1):
if (df or dr) and at(f+df,r+dr)==K: return True
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))):
ff,rr=f+df,r+dr
while 0<=ff<8 and 0<=rr<8:
v=at(ff,rr)
if v:
if v in kinds: return True
break
ff+=df; rr+=dr
return False
b=x['board']; fr,to=x['from'],x['to']; k=b[fr]; white=k=='K'
df=ord(to[0])-ord(fr[0]); dr=int(to[1])-int(fr[1])
if max(abs(df),abs(dr))!=1: return False
occ=b.get(to)
if occ and occ.isupper()==white: return False
nb=dict(b); nb[to]=nb.pop(fr) if not occ else k
return not attacked(nb, to, not white)
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('retreat along rook file',
{'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),
('sidestep rook file', {'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'd3'},
True),
('diagonal step', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'f5'}, True),
('stand still', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e4'}, False),
('capture own', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'P'}, 'from': 'e4', 'to': 'e5'}, False),
('capture undefended', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'p'}, 'from': 'e4', 'to': 'e5'},
True),
('black king bishop diag retreat',
{'board': {'b3': 'B', 'd5': 'k', 'h1': 'K'}, 'from': 'd5', 'to': 'e6'}, False),
('capture along check line',
{'board': {'a1': 'k', 'e3': 'p', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False)],
[('capture own', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'P'}, 'from': 'e4', 'to': 'e5'}, False),
('capture undefended', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'p'}, 'from': 'e4', 'to': 'e5'},
True),
('capture defended',
{'board': {'a8': 'k', 'd6': 'p', 'e4': 'K', 'e5': 'p'}, 'from': 'e4', 'to': 'e5'}, False),
('next to enemy king orthogonal', {'board': {'e4': 'K', 'e6': 'k'}, 'from': 'e4', 'to': 'e5'},
False),
('next to enemy king diagonal', {'board': {'e4': 'K', 'g6': 'k'}, 'from': 'e4', 'to': 'f5'},
False),
('knight below', {'board': {'a8': 'k', 'e4': 'K', 'f1': 'n'}, 'from': 'e4', 'to': 'e3'}, False),
('black king bishop diag retreat',
{'board': {'b3': 'B', 'd5': 'k', 'h1': 'K'}, 'from': 'd5', 'to': 'e6'}, False),
('capture along check line',
{'board': {'a1': 'k', 'e3': 'p', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False)],
[('retreat along rook file',
{'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),
('next to enemy king orthogonal', {'board': {'e4': 'K', 'e6': 'k'}, 'from': 'e4', 'to': 'e5'},
False),
('next to enemy king diagonal', {'board': {'e4': 'K', 'g6': 'k'}, 'from': 'e4', 'to': 'f5'},
False),
('knight below', {'board': {'a8': 'k', 'e4': 'K', 'f1': 'n'}, 'from': 'e4', 'to': 'e3'}, False),
('knight above', {'board': {'a8': 'k', 'd7': 'n', 'e4': 'K'}, 'from': 'e4', 'to': 'e5'}, False),
('capture along check line',
{'board': {'a1': 'k', 'e3': 'p', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),
('capture defended knight',
{'board': {'a8': 'k', 'e4': 'K', 'e5': 'n', 'e7': 'r'}, 'from': 'e4', 'to': 'e5'}, False),
('two squares', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e6'}, False)],
[('retreat along rook file',
{'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),
('sidestep rook file', {'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'd3'},
True),
('knight above', {'board': {'a8': 'k', 'd7': 'n', 'e4': 'K'}, 'from': 'e4', 'to': 'e5'}, False),
('black king bishop diag retreat',
{'board': {'b3': 'B', 'd5': 'k', 'h1': 'K'}, 'from': 'd5', 'to': 'e6'}, False),
('capture along check line',
{'board': {'a1': 'k', 'e3': 'p', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),
('capture defended knight',
{'board': {'a8': 'k', 'e4': 'K', 'e5': 'n', 'e7': 'r'}, 'from': 'e4', 'to': 'e5'}, False),
('two squares', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e6'}, False),
('knight far below', {'board': {'a8': 'k', 'c4': 'n', 'e4': 'K'}, 'from': 'e4', 'to': 'd3'},
True)],
[('retreat along rook file',
{'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),
('sidestep rook file', {'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'd3'},
True),
('diagonal step', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'f5'}, True),
('stand still', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e4'}, False),
('capture own', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'P'}, 'from': 'e4', 'to': 'e5'}, False),
('black king bishop diag retreat',
{'board': {'b3': 'B', 'd5': 'k', 'h1': 'K'}, 'from': 'd5', 'to': 'e6'}, False),
('capture along check line',
{'board': {'a1': 'k', 'e3': 'p', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),
('knight far below', {'board': {'a8': 'k', 'c4': 'n', 'e4': 'K'}, 'from': 'e4', 'to': 'd3'},
True)]]
for label, args, expected in fixtures[N-1]:
try:
actual = solve(args)
except Exception as exc:
actual = 'error:' + type(exc).__name__
check(label, actual, expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| retreat along rook file | False | False | Passed |
| sidestep rook file | True | True | Passed |
| diagonal step | True | True | Passed |
| stand still | False | False | Passed |
| capture own | False | False | Passed |
| capture undefended | True | True | Passed |
| black king bishop diag retreat | False | False | Passed |
| capture along check line | True | False | Failed |
SHA-256 / 4033c8573b6c55c1f381c77934a4a57ff26ed03357ade476875e6a8cb27b164e
3 / The verified repair
Exit 0"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(x):
def attacked(bd, sq, by_white):
f,r=ord(sq[0])-97,int(sq[1])-1
def at(ff,rr):
return bd.get(chr(97+ff)+str(rr+1)) if 0<=ff<8 and 0<=rr<8 else None
P,N,B,R,Q,K=('PNBRQK' if by_white else 'pnbrqk')
pr=r-1 if by_white else r+1
if at(f-1,pr)==P or at(f+1,pr)==P: return True
for df,dr in ((1,2),(2,1),(-1,2),(-2,1),(1,-2),(2,-1),(-1,-2),(-2,-1)):
if at(f+df,r+dr)==N: return True
for df in (-1,0,1):
for dr in (-1,0,1):
if (df or dr) and at(f+df,r+dr)==K: return True
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))):
ff,rr=f+df,r+dr
while 0<=ff<8 and 0<=rr<8:
v=at(ff,rr)
if v:
if v in kinds: return True
break
ff+=df; rr+=dr
return False
b=x['board']; fr,to=x['from'],x['to']; k=b[fr]; white=k=='K'
df=ord(to[0])-ord(fr[0]); dr=int(to[1])-int(fr[1])
if max(abs(df),abs(dr))!=1: return False
occ=b.get(to)
if occ and occ.isupper()==white: return False
nb=dict(b); del nb[fr]; nb[to]=k
return not attacked(nb, to, not white)
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('retreat along rook file',
{'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),
('sidestep rook file', {'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'd3'},
True),
('diagonal step', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'f5'}, True),
('stand still', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e4'}, False),
('capture own', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'P'}, 'from': 'e4', 'to': 'e5'}, False),
('capture undefended', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'p'}, 'from': 'e4', 'to': 'e5'},
True),
('black king bishop diag retreat',
{'board': {'b3': 'B', 'd5': 'k', 'h1': 'K'}, 'from': 'd5', 'to': 'e6'}, False),
('capture along check line',
{'board': {'a1': 'k', 'e3': 'p', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False)],
[('capture own', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'P'}, 'from': 'e4', 'to': 'e5'}, False),
('capture undefended', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'p'}, 'from': 'e4', 'to': 'e5'},
True),
('capture defended',
{'board': {'a8': 'k', 'd6': 'p', 'e4': 'K', 'e5': 'p'}, 'from': 'e4', 'to': 'e5'}, False),
('next to enemy king orthogonal', {'board': {'e4': 'K', 'e6': 'k'}, 'from': 'e4', 'to': 'e5'},
False),
('next to enemy king diagonal', {'board': {'e4': 'K', 'g6': 'k'}, 'from': 'e4', 'to': 'f5'},
False),
('knight below', {'board': {'a8': 'k', 'e4': 'K', 'f1': 'n'}, 'from': 'e4', 'to': 'e3'}, False),
('black king bishop diag retreat',
{'board': {'b3': 'B', 'd5': 'k', 'h1': 'K'}, 'from': 'd5', 'to': 'e6'}, False),
('capture along check line',
{'board': {'a1': 'k', 'e3': 'p', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False)],
[('retreat along rook file',
{'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),
('next to enemy king orthogonal', {'board': {'e4': 'K', 'e6': 'k'}, 'from': 'e4', 'to': 'e5'},
False),
('next to enemy king diagonal', {'board': {'e4': 'K', 'g6': 'k'}, 'from': 'e4', 'to': 'f5'},
False),
('knight below', {'board': {'a8': 'k', 'e4': 'K', 'f1': 'n'}, 'from': 'e4', 'to': 'e3'}, False),
('knight above', {'board': {'a8': 'k', 'd7': 'n', 'e4': 'K'}, 'from': 'e4', 'to': 'e5'}, False),
('capture along check line',
{'board': {'a1': 'k', 'e3': 'p', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),
('capture defended knight',
{'board': {'a8': 'k', 'e4': 'K', 'e5': 'n', 'e7': 'r'}, 'from': 'e4', 'to': 'e5'}, False),
('two squares', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e6'}, False)],
[('retreat along rook file',
{'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),
('sidestep rook file', {'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'd3'},
True),
('knight above', {'board': {'a8': 'k', 'd7': 'n', 'e4': 'K'}, 'from': 'e4', 'to': 'e5'}, False),
('black king bishop diag retreat',
{'board': {'b3': 'B', 'd5': 'k', 'h1': 'K'}, 'from': 'd5', 'to': 'e6'}, False),
('capture along check line',
{'board': {'a1': 'k', 'e3': 'p', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),
('capture defended knight',
{'board': {'a8': 'k', 'e4': 'K', 'e5': 'n', 'e7': 'r'}, 'from': 'e4', 'to': 'e5'}, False),
('two squares', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e6'}, False),
('knight far below', {'board': {'a8': 'k', 'c4': 'n', 'e4': 'K'}, 'from': 'e4', 'to': 'd3'},
True)],
[('retreat along rook file',
{'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),
('sidestep rook file', {'board': {'a1': 'k', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'd3'},
True),
('diagonal step', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'f5'}, True),
('stand still', {'board': {'a8': 'k', 'e4': 'K'}, 'from': 'e4', 'to': 'e4'}, False),
('capture own', {'board': {'a8': 'k', 'e4': 'K', 'e5': 'P'}, 'from': 'e4', 'to': 'e5'}, False),
('black king bishop diag retreat',
{'board': {'b3': 'B', 'd5': 'k', 'h1': 'K'}, 'from': 'd5', 'to': 'e6'}, False),
('capture along check line',
{'board': {'a1': 'k', 'e3': 'p', 'e4': 'K', 'e8': 'r'}, 'from': 'e4', 'to': 'e3'}, False),
('knight far below', {'board': {'a8': 'k', 'c4': 'n', 'e4': 'K'}, 'from': 'e4', 'to': 'd3'},
True)]]
for label, args, expected in fixtures[N-1]:
try:
actual = solve(args)
except Exception as exc:
actual = 'error:' + type(exc).__name__
check(label, actual, expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| retreat along rook file | False | False | Passed |
| sidestep rook file | True | True | Passed |
| diagonal step | True | True | Passed |
| stand still | False | False | Passed |
| capture own | False | False | Passed |
| capture undefended | True | True | Passed |
| black king bishop diag retreat | False | False | Passed |
| capture along check line | False | False | Passed |
SHA-256 / ce98a81337870ebebc4984db6a8c1ecefb268b87d6f385d3cf690d7d4effbfc6
Verification & scope
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.
Observations recorded using Python 3.12.14 at 2026-09-29T14:50:12.403361+00:00.
Case digest / 1cefff6a72e516f753f471fce91d66fdfe60787447d2aeb41406fe68e770dfdd