FAILURE MAP
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FA-80476 / Bidirectional text layout / Open access

Visual reordering by levels: reversal loop bound · case 01

Runs at the lowest odd level stay in logical order.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The level loop excludes its lower bound.

VERIFIED REPAIR

Include the lowest odd level in the loop.

Unsuccessful approach: Starting one below the highest level skips the top pass.

Case contract

Input resolved levels of one line. From the highest level down to the lowest odd level on the line, reverse every maximal visual run of characters at that level or higher. Return logical indices in visual order (identity when no odd level).

Why this case matters

Mixed right-to-left and left-to-right text must resolve levels and visual order exactly, or words, numbers and carets land in the wrong place.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    levels = x
    order = list(range(len(levels)))
    odd = [l for l in levels if l % 2 == 1]
    if not odd:
        return order
    hi = max(levels)
    lo = min(odd)
    vis = [[lv, i] for i, lv in enumerate(levels)]
    for lev in range(hi, lo, -1):
        i = 0
        while i < len(vis):
            if vis[i][0] >= lev:
                j = i
                while j < len(vis) and vis[j][0] >= lev:
                    j += 1
                vis[i:j] = vis[i:j][::-1]
                i = j
            else:
                i += 1
    return [p[1] for p in vis]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('number inside RTL', [1, 1, 2, 2, 1], [4, 2, 3, 1, 0]), ('regression: reversal loop bound', [3, 3, 3, 3, 1, 1, 1, 3, 3, 3], [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]), ('regression: reversal loop bound', [3, 3, 3, 0, 0, 0, 2, 2, 2, 2], [2, 1, 0, 3, 4, 5, 6, 7, 8, 9]), ('regression: reversal loop bound', [1, 1, 2, 2, 3, 3, 2, 2], [2, 3, 5, 4, 6, 7, 1, 0]), ('lowest odd is three', [2, 3, 3, 2], [0, 2, 1, 3]), ('all even levels', [0, 2, 2, 0], [0, 1, 2, 3]), ('control layout', [0, 0, 0, 0, 0, 0, 0, 0], [0, 1, 2, 3, 4, 5, 6, 7]), ('control layout', [2], [0])], [('regression: reversal loop bound', [1, 1, 1, 1, 1, 1], [5, 4, 3, 2, 1, 0]), ('regression: reversal loop bound', [1, 1, 1], [2, 1, 0]), ('regression: reversal loop bound', [3, 0, 3, 3, 3, 3], [0, 1, 5, 4, 3, 2]), ('regression: reversal loop bound', [2, 2, 1, 1, 1], [4, 3, 2, 0, 1]), ('all even levels', [0, 2, 2, 0], [0, 1, 2, 3]), ('number inside RTL', [1, 1, 2, 2, 1], [4, 2, 3, 1, 0]), ('control layout', [2, 2, 2], [0, 1, 2]), ('control layout', [2, 2], [0, 1])], [('regression: reversal loop bound', [1, 0, 0, 0, 2, 2, 2, 0, 2], [0, 1, 2, 3, 4, 5, 6, 7, 8]), ('regression: reversal loop bound', [2, 2, 2, 0, 0, 1, 1, 1, 1, 1], [0, 1, 2, 3, 4, 9, 8, 7, 6, 5]), ('regression: reversal loop bound', [4, 4, 4, 1, 1, 1, 2], [6, 5, 4, 3, 0, 1, 2]), ('regression: reversal loop bound', [3, 3, 2, 2, 2, 2, 1, 1, 1], [8, 7, 6, 1, 0, 2, 3, 4, 5]), ('number inside RTL', [1, 1, 2, 2, 1], [4, 2, 3, 1, 0]), ('lowest odd is three', [2, 3, 3, 2], [0, 2, 1, 3]), ('control layout', [2, 2], [0, 1]), ('control layout', [4, 4], [0, 1])], [('regression: reversal loop bound', [1, 1, 1], [2, 1, 0]), ('regression: reversal loop bound', [1, 1, 1, 0, 0, 0, 0, 0, 0, 1], [2, 1, 0, 3, 4, 5, 6, 7, 8, 9]), ('regression: reversal loop bound', [0, 0, 0, 2, 0, 3, 3], [0, 1, 2, 3, 4, 6, 5]), ('regression: reversal loop bound', [1, 1, 1, 2, 2, 2], [3, 4, 5, 2, 1, 0]), ('all even levels', [0, 2, 2, 0], [0, 1, 2, 3]), ('lowest odd is three', [2, 3, 3, 2], [0, 2, 1, 3]), ('control layout', [1], [0]), ('control layout', [0, 0, 0, 0, 0], [0, 1, 2, 3, 4])], [('regression: reversal loop bound', [3, 1, 1, 2, 2], [3, 4, 2, 1, 0]), ('regression: reversal loop bound', [2, 2, 2, 2, 1, 1, 1, 1, 1], [8, 7, 6, 5, 4, 0, 1, 2, 3]), ('regression: reversal loop bound', [1, 1, 1, 3, 3, 3], [5, 4, 3, 2, 1, 0]), ('regression: reversal loop bound', [3, 2, 2, 2, 1, 1, 1, 4, 4, 4, 4, 1], [11, 7, 8, 9, 10, 6, 5, 4, 0, 1, 2, 3]), ('number inside RTL', [1, 1, 2, 2, 1], [4, 2, 3, 1, 0]), ('lowest odd is three', [2, 3, 3, 2], [0, 2, 1, 3]), ('control layout', [2], [0]), ('control layout', [0, 0, 0, 0, 0, 0, 0, 2, 2, 2, 2], [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10])]]
for label, args, expected in fixtures[N - 1]:
    check(label, solve(args), 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 fixtureActualExpectedOutcome
number inside RTL[0, 1, 3, 2, 4][4, 2, 3, 1, 0]Failed
regression: reversal loop bound[0, 1, 2, 3, 4, 5, 6, 7, 8, 9][9, 8, 7, 6, 5, 4, 3, 2, 1, 0]Failed
regression: reversal loop bound[0, 1, 2, 3, 4, 5, 6, 7, 8, 9][2, 1, 0, 3, 4, 5, 6, 7, 8, 9]Failed
regression: reversal loop bound[0, 1, 7, 6, 4, 5, 3, 2][2, 3, 5, 4, 6, 7, 1, 0]Failed
lowest odd is three[0, 1, 2, 3][0, 2, 1, 3]Failed
all even levels[0, 1, 2, 3][0, 1, 2, 3]Passed
control layout[0, 1, 2, 3, 4, 5, 6, 7][0, 1, 2, 3, 4, 5, 6, 7]Passed
control layout[0][0]Passed

SHA-256 / a9fe41627ddf3f3e197538d9b574c5a67c1eaa1cd3ae10427fdd4d6b230aed7c

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    levels = x
    order = list(range(len(levels)))
    odd = [l for l in levels if l % 2 == 1]
    if not odd:
        return order
    hi = max(levels)
    lo = min(odd)
    vis = [[lv, i] for i, lv in enumerate(levels)]
    for lev in range(hi - 1, lo - 1, -1):
        i = 0
        while i < len(vis):
            if vis[i][0] >= lev:
                j = i
                while j < len(vis) and vis[j][0] >= lev:
                    j += 1
                vis[i:j] = vis[i:j][::-1]
                i = j
            else:
                i += 1
    return [p[1] for p in vis]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('number inside RTL', [1, 1, 2, 2, 1], [4, 2, 3, 1, 0]), ('regression: reversal loop bound', [3, 3, 3, 3, 1, 1, 1, 3, 3, 3], [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]), ('regression: reversal loop bound', [3, 3, 3, 0, 0, 0, 2, 2, 2, 2], [2, 1, 0, 3, 4, 5, 6, 7, 8, 9]), ('regression: reversal loop bound', [1, 1, 2, 2, 3, 3, 2, 2], [2, 3, 5, 4, 6, 7, 1, 0]), ('lowest odd is three', [2, 3, 3, 2], [0, 2, 1, 3]), ('all even levels', [0, 2, 2, 0], [0, 1, 2, 3]), ('control layout', [0, 0, 0, 0, 0, 0, 0, 0], [0, 1, 2, 3, 4, 5, 6, 7]), ('control layout', [2], [0])], [('regression: reversal loop bound', [1, 1, 1, 1, 1, 1], [5, 4, 3, 2, 1, 0]), ('regression: reversal loop bound', [1, 1, 1], [2, 1, 0]), ('regression: reversal loop bound', [3, 0, 3, 3, 3, 3], [0, 1, 5, 4, 3, 2]), ('regression: reversal loop bound', [2, 2, 1, 1, 1], [4, 3, 2, 0, 1]), ('all even levels', [0, 2, 2, 0], [0, 1, 2, 3]), ('number inside RTL', [1, 1, 2, 2, 1], [4, 2, 3, 1, 0]), ('control layout', [2, 2, 2], [0, 1, 2]), ('control layout', [2, 2], [0, 1])], [('regression: reversal loop bound', [1, 0, 0, 0, 2, 2, 2, 0, 2], [0, 1, 2, 3, 4, 5, 6, 7, 8]), ('regression: reversal loop bound', [2, 2, 2, 0, 0, 1, 1, 1, 1, 1], [0, 1, 2, 3, 4, 9, 8, 7, 6, 5]), ('regression: reversal loop bound', [4, 4, 4, 1, 1, 1, 2], [6, 5, 4, 3, 0, 1, 2]), ('regression: reversal loop bound', [3, 3, 2, 2, 2, 2, 1, 1, 1], [8, 7, 6, 1, 0, 2, 3, 4, 5]), ('number inside RTL', [1, 1, 2, 2, 1], [4, 2, 3, 1, 0]), ('lowest odd is three', [2, 3, 3, 2], [0, 2, 1, 3]), ('control layout', [2, 2], [0, 1]), ('control layout', [4, 4], [0, 1])], [('regression: reversal loop bound', [1, 1, 1], [2, 1, 0]), ('regression: reversal loop bound', [1, 1, 1, 0, 0, 0, 0, 0, 0, 1], [2, 1, 0, 3, 4, 5, 6, 7, 8, 9]), ('regression: reversal loop bound', [0, 0, 0, 2, 0, 3, 3], [0, 1, 2, 3, 4, 6, 5]), ('regression: reversal loop bound', [1, 1, 1, 2, 2, 2], [3, 4, 5, 2, 1, 0]), ('all even levels', [0, 2, 2, 0], [0, 1, 2, 3]), ('lowest odd is three', [2, 3, 3, 2], [0, 2, 1, 3]), ('control layout', [1], [0]), ('control layout', [0, 0, 0, 0, 0], [0, 1, 2, 3, 4])], [('regression: reversal loop bound', [3, 1, 1, 2, 2], [3, 4, 2, 1, 0]), ('regression: reversal loop bound', [2, 2, 2, 2, 1, 1, 1, 1, 1], [8, 7, 6, 5, 4, 0, 1, 2, 3]), ('regression: reversal loop bound', [1, 1, 1, 3, 3, 3], [5, 4, 3, 2, 1, 0]), ('regression: reversal loop bound', [3, 2, 2, 2, 1, 1, 1, 4, 4, 4, 4, 1], [11, 7, 8, 9, 10, 6, 5, 4, 0, 1, 2, 3]), ('number inside RTL', [1, 1, 2, 2, 1], [4, 2, 3, 1, 0]), ('lowest odd is three', [2, 3, 3, 2], [0, 2, 1, 3]), ('control layout', [2], [0]), ('control layout', [0, 0, 0, 0, 0, 0, 0, 2, 2, 2, 2], [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10])]]
for label, args, expected in fixtures[N - 1]:
    check(label, solve(args), 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 fixtureActualExpectedOutcome
number inside RTL[4, 3, 2, 1, 0][4, 2, 3, 1, 0]Failed
regression: reversal loop bound[7, 8, 9, 6, 5, 4, 0, 1, 2, 3][9, 8, 7, 6, 5, 4, 3, 2, 1, 0]Failed
regression: reversal loop bound[0, 1, 2, 3, 4, 5, 6, 7, 8, 9][2, 1, 0, 3, 4, 5, 6, 7, 8, 9]Failed
regression: reversal loop bound[2, 3, 4, 5, 6, 7, 1, 0][2, 3, 5, 4, 6, 7, 1, 0]Failed
lowest odd is three[0, 1, 2, 3][0, 2, 1, 3]Failed
all even levels[0, 1, 2, 3][0, 1, 2, 3]Passed
control layout[0, 1, 2, 3, 4, 5, 6, 7][0, 1, 2, 3, 4, 5, 6, 7]Passed
control layout[0][0]Passed

SHA-256 / 5139651ec313046be82339159ca2cc5893820e5ed977cc89ab840e07f9d69ef6

3 / The verified repair

Exit 0
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    levels = x
    order = list(range(len(levels)))
    odd = [l for l in levels if l % 2 == 1]
    if not odd:
        return order
    hi = max(levels)
    lo = min(odd)
    vis = [[lv, i] for i, lv in enumerate(levels)]
    for lev in range(hi, lo - 1, -1):
        i = 0
        while i < len(vis):
            if vis[i][0] >= lev:
                j = i
                while j < len(vis) and vis[j][0] >= lev:
                    j += 1
                vis[i:j] = vis[i:j][::-1]
                i = j
            else:
                i += 1
    return [p[1] for p in vis]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('number inside RTL', [1, 1, 2, 2, 1], [4, 2, 3, 1, 0]), ('regression: reversal loop bound', [3, 3, 3, 3, 1, 1, 1, 3, 3, 3], [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]), ('regression: reversal loop bound', [3, 3, 3, 0, 0, 0, 2, 2, 2, 2], [2, 1, 0, 3, 4, 5, 6, 7, 8, 9]), ('regression: reversal loop bound', [1, 1, 2, 2, 3, 3, 2, 2], [2, 3, 5, 4, 6, 7, 1, 0]), ('lowest odd is three', [2, 3, 3, 2], [0, 2, 1, 3]), ('all even levels', [0, 2, 2, 0], [0, 1, 2, 3]), ('control layout', [0, 0, 0, 0, 0, 0, 0, 0], [0, 1, 2, 3, 4, 5, 6, 7]), ('control layout', [2], [0])], [('regression: reversal loop bound', [1, 1, 1, 1, 1, 1], [5, 4, 3, 2, 1, 0]), ('regression: reversal loop bound', [1, 1, 1], [2, 1, 0]), ('regression: reversal loop bound', [3, 0, 3, 3, 3, 3], [0, 1, 5, 4, 3, 2]), ('regression: reversal loop bound', [2, 2, 1, 1, 1], [4, 3, 2, 0, 1]), ('all even levels', [0, 2, 2, 0], [0, 1, 2, 3]), ('number inside RTL', [1, 1, 2, 2, 1], [4, 2, 3, 1, 0]), ('control layout', [2, 2, 2], [0, 1, 2]), ('control layout', [2, 2], [0, 1])], [('regression: reversal loop bound', [1, 0, 0, 0, 2, 2, 2, 0, 2], [0, 1, 2, 3, 4, 5, 6, 7, 8]), ('regression: reversal loop bound', [2, 2, 2, 0, 0, 1, 1, 1, 1, 1], [0, 1, 2, 3, 4, 9, 8, 7, 6, 5]), ('regression: reversal loop bound', [4, 4, 4, 1, 1, 1, 2], [6, 5, 4, 3, 0, 1, 2]), ('regression: reversal loop bound', [3, 3, 2, 2, 2, 2, 1, 1, 1], [8, 7, 6, 1, 0, 2, 3, 4, 5]), ('number inside RTL', [1, 1, 2, 2, 1], [4, 2, 3, 1, 0]), ('lowest odd is three', [2, 3, 3, 2], [0, 2, 1, 3]), ('control layout', [2, 2], [0, 1]), ('control layout', [4, 4], [0, 1])], [('regression: reversal loop bound', [1, 1, 1], [2, 1, 0]), ('regression: reversal loop bound', [1, 1, 1, 0, 0, 0, 0, 0, 0, 1], [2, 1, 0, 3, 4, 5, 6, 7, 8, 9]), ('regression: reversal loop bound', [0, 0, 0, 2, 0, 3, 3], [0, 1, 2, 3, 4, 6, 5]), ('regression: reversal loop bound', [1, 1, 1, 2, 2, 2], [3, 4, 5, 2, 1, 0]), ('all even levels', [0, 2, 2, 0], [0, 1, 2, 3]), ('lowest odd is three', [2, 3, 3, 2], [0, 2, 1, 3]), ('control layout', [1], [0]), ('control layout', [0, 0, 0, 0, 0], [0, 1, 2, 3, 4])], [('regression: reversal loop bound', [3, 1, 1, 2, 2], [3, 4, 2, 1, 0]), ('regression: reversal loop bound', [2, 2, 2, 2, 1, 1, 1, 1, 1], [8, 7, 6, 5, 4, 0, 1, 2, 3]), ('regression: reversal loop bound', [1, 1, 1, 3, 3, 3], [5, 4, 3, 2, 1, 0]), ('regression: reversal loop bound', [3, 2, 2, 2, 1, 1, 1, 4, 4, 4, 4, 1], [11, 7, 8, 9, 10, 6, 5, 4, 0, 1, 2, 3]), ('number inside RTL', [1, 1, 2, 2, 1], [4, 2, 3, 1, 0]), ('lowest odd is three', [2, 3, 3, 2], [0, 2, 1, 3]), ('control layout', [2], [0]), ('control layout', [0, 0, 0, 0, 0, 0, 0, 2, 2, 2, 2], [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10])]]
for label, args, expected in fixtures[N - 1]:
    check(label, solve(args), 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 fixtureActualExpectedOutcome
number inside RTL[4, 2, 3, 1, 0][4, 2, 3, 1, 0]Passed
regression: reversal loop bound[9, 8, 7, 6, 5, 4, 3, 2, 1, 0][9, 8, 7, 6, 5, 4, 3, 2, 1, 0]Passed
regression: reversal loop bound[2, 1, 0, 3, 4, 5, 6, 7, 8, 9][2, 1, 0, 3, 4, 5, 6, 7, 8, 9]Passed
regression: reversal loop bound[2, 3, 5, 4, 6, 7, 1, 0][2, 3, 5, 4, 6, 7, 1, 0]Passed
lowest odd is three[0, 2, 1, 3][0, 2, 1, 3]Passed
all even levels[0, 1, 2, 3][0, 1, 2, 3]Passed
control layout[0, 1, 2, 3, 4, 5, 6, 7][0, 1, 2, 3, 4, 5, 6, 7]Passed
control layout[0][0]Passed

SHA-256 / 7dcf205b45a5525ab0e2de7a7adcb8a29be3892fc7be9730223a294904695b8a

Verification & scope

A deterministic toy bidi model over stipulated class labels and integer levels; it is inspired by, but does not claim conformance to, any published algorithm. 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 2026-09-29T14:49:54.185948+00:00.

Case digest / f4894e3c05d6a060a3168f71c6e59a72efa135a829ee4ce63e9ee079cfaddd57