FAILURE MAP
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FA-88706 / Mesh topology invariants / Open access

Operator sequence may leave a face without a loop · case 01

Sequences that give a face no bounding loop are accepted.

Verified by executionVariant 1 · 7 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Validity only checks for negative counts, not L >= F.

THE FAILURE

Validity only checks for negative counts, not L >= F.

Unsuccessful approach: Allowing one loop deficit still accepts faces without loops.

Case contract

Input: list of Euler operator names applied to counts [V,E,F,L,S,G] starting at zero. Deltas: mvfs(+V,+F,+L,+S), mev(+V,+E), mef(+E,+F,+L), kemr(-E,+L), mekr(+E,-L), kfmrh(-F,+G) and their inverses kvfs, kev, kef, mfkrh. After each op: an unknown name returns ["unknown", i]; a negative count or fewer loops than faces returns ["invalid", i]; a violated Euler-Poincare relation V-E+F-(L-F)=2(S-G) returns ["broken-invariant", i]. Return the final counts.

Why this case matters

Mesh processing pipelines (remeshing, export, simulation, printing) trust these topological counts and adjacency answers; a wrong invariant silently accepts broken meshes or rejects valid ones.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(x):
    ops=x
    V=E=Fc=L=S=G=0
    D={'mvfs':(1,0,1,1,1,0),'kvfs':(-1,0,-1,-1,-1,0),'mev':(1,1,0,0,0,0),'kev':(-1,-1,0,0,0,0),
       'mef':(0,1,1,1,0,0),'kef':(0,-1,-1,-1,0,0),'kemr':(0,-1,0,1,0,0),'mekr':(0,1,0,-1,0,0),
       'kfmrh':(0,0,-1,0,0,1),'mfkrh':(0,0,1,0,0,-1)}
    for i,op in enumerate(ops):
        if op not in D: return ['unknown',i]
        d=D[op]
        V,E,Fc,L,S,G=V+d[0],E+d[1],Fc+d[2],L+d[3],S+d[4],G+d[5]
        if min(V,E,Fc,L,S,G)<0: return ['invalid',i]
        if V-E+Fc-(L-Fc)!=2*(S-G): return ['broken-invariant',i]
    return [V,E,Fc,L,S,G]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['triangle lamina', [['mvfs', 'mev', 'mev', 'mef']], [3, 3, 2, 2, 1, 0]], ['tetrahedron', [['mvfs', 'mev', 'mev', 'mef', 'mev', 'mef', 'mef']], [4, 6, 4, 4, 1, 0]], ['square with hole ring', [['mvfs', 'mev', 'mev', 'mev', 'mef', 'mev', 'mev', 'mev', 'mef', 'kemr']], [7, 7, 3, 4, 1, 0]], ['torus handle', [['mvfs', 'mev', 'mev', 'mev', 'mef', 'mev', 'mev', 'mev', 'mef', 'kemr', 'kfmrh']], [7, 7, 2, 4, 1, 1]], ['undo handle', [['mvfs', 'mev', 'mev', 'mev', 'mef', 'mev', 'mev', 'mev', 'mef', 'kemr', 'kfmrh', 'mfkrh']], [7, 7, 3, 4, 1, 0]], ['ring then remake edge', [['mvfs', 'mev', 'mev', 'mef', 'mev', 'kemr', 'mekr']], [4, 4, 2, 2, 1, 0]], ['loop deficit', [['mvfs', 'mev', 'mekr']], ['invalid', 2]]], [['torus handle', [['mvfs', 'mev', 'mev', 'mev', 'mef', 'mev', 'mev', 'mev', 'mef', 'kemr', 'kfmrh']], [7, 7, 2, 4, 1, 1]], ['undo handle', [['mvfs', 'mev', 'mev', 'mev', 'mef', 'mev', 'mev', 'mev', 'mef', 'kemr', 'kfmrh', 'mfkrh']], [7, 7, 3, 4, 1, 0]], ['ring then remake edge', [['mvfs', 'mev', 'mev', 'mef', 'mev', 'kemr', 'mekr']], [4, 4, 2, 2, 1, 0]], ['kill edge on empty', [['mvfs', 'kev']], ['invalid', 1]], ['unknown op', [['mvfs', 'mev', 'split']], ['unknown', 2]], ['uppercase op', [['mvfs', 'MEV']], ['unknown', 1]], ['loop deficit', [['mvfs', 'mev', 'mekr']], ['invalid', 2]]], [['kill edge on empty', [['mvfs', 'kev']], ['invalid', 1]], ['unknown op', [['mvfs', 'mev', 'split']], ['unknown', 2]], ['uppercase op', [['mvfs', 'MEV']], ['unknown', 1]], ['loop deficit', [['mvfs', 'mev', 'mekr']], ['invalid', 2]], ['two shells', [['mvfs', 'mev', 'mvfs', 'mev', 'mev', 'mef']], [5, 4, 3, 3, 2, 0]], ['face without loop', [['mvfs', 'mfkrh']], ['invalid', 1]], ['build and kill', [['mvfs', 'mev', 'mev', 'mef', 'kef', 'kev', 'kev', 'kvfs']], [0, 0, 0, 0, 0, 0]]], [['triangle lamina', [['mvfs', 'mev', 'mev', 'mef']], [3, 3, 2, 2, 1, 0]], ['tetrahedron', [['mvfs', 'mev', 'mev', 'mef', 'mev', 'mef', 'mef']], [4, 6, 4, 4, 1, 0]], ['loop deficit', [['mvfs', 'mev', 'mekr']], ['invalid', 2]], ['two shells', [['mvfs', 'mev', 'mvfs', 'mev', 'mev', 'mef']], [5, 4, 3, 3, 2, 0]], ['face without loop', [['mvfs', 'mfkrh']], ['invalid', 1]], ['build and kill', [['mvfs', 'mev', 'mev', 'mef', 'kef', 'kev', 'kev', 'kvfs']], [0, 0, 0, 0, 0, 0]], ['hole into lamina', [['mvfs', 'mev', 'mev', 'mef', 'mev', 'mev', 'mev', 'mef', 'kemr', 'kfmrh', 'mev']], [7, 7, 2, 4, 1, 1]]], [['triangle lamina', [['mvfs', 'mev', 'mev', 'mef']], [3, 3, 2, 2, 1, 0]], ['tetrahedron', [['mvfs', 'mev', 'mev', 'mef', 'mev', 'mef', 'mef']], [4, 6, 4, 4, 1, 0]], ['square with hole ring', [['mvfs', 'mev', 'mev', 'mev', 'mef', 'mev', 'mev', 'mev', 'mef', 'kemr']], [7, 7, 3, 4, 1, 0]], ['torus handle', [['mvfs', 'mev', 'mev', 'mev', 'mef', 'mev', 'mev', 'mev', 'mef', 'kemr', 'kfmrh']], [7, 7, 2, 4, 1, 1]], ['undo handle', [['mvfs', 'mev', 'mev', 'mev', 'mef', 'mev', 'mev', 'mev', 'mef', 'kemr', 'kfmrh', 'mfkrh']], [7, 7, 3, 4, 1, 0]], ['loop deficit', [['mvfs', 'mev', 'mekr']], ['invalid', 2]], ['hole into lamina', [['mvfs', 'mev', 'mev', 'mef', 'mev', 'mev', 'mev', 'mef', 'kemr', 'kfmrh', 'mev']], [7, 7, 2, 4, 1, 1]]]]
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
triangle lamina[3, 3, 2, 2, 1, 0][3, 3, 2, 2, 1, 0]Passed
tetrahedron[4, 6, 4, 4, 1, 0][4, 6, 4, 4, 1, 0]Passed
square with hole ring[7, 7, 3, 4, 1, 0][7, 7, 3, 4, 1, 0]Passed
torus handle[7, 7, 2, 4, 1, 1][7, 7, 2, 4, 1, 1]Passed
undo handle[7, 7, 3, 4, 1, 0][7, 7, 3, 4, 1, 0]Passed
ring then remake edge[4, 4, 2, 2, 1, 0][4, 4, 2, 2, 1, 0]Passed
loop deficit[2, 2, 1, 0, 1, 0]['invalid', 2]Failed

SHA-256 / b4c7b0e8f031f5ee78704439a145f67211497935e7ddbab91c5286dffa80e158

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(x):
    ops=x
    V=E=Fc=L=S=G=0
    D={'mvfs':(1,0,1,1,1,0),'kvfs':(-1,0,-1,-1,-1,0),'mev':(1,1,0,0,0,0),'kev':(-1,-1,0,0,0,0),
       'mef':(0,1,1,1,0,0),'kef':(0,-1,-1,-1,0,0),'kemr':(0,-1,0,1,0,0),'mekr':(0,1,0,-1,0,0),
       'kfmrh':(0,0,-1,0,0,1),'mfkrh':(0,0,1,0,0,-1)}
    for i,op in enumerate(ops):
        if op not in D: return ['unknown',i]
        d=D[op]
        V,E,Fc,L,S,G=V+d[0],E+d[1],Fc+d[2],L+d[3],S+d[4],G+d[5]
        if min(V,E,Fc,L,S,G)<0 or L<Fc-1: return ['invalid',i]
        if V-E+Fc-(L-Fc)!=2*(S-G): return ['broken-invariant',i]
    return [V,E,Fc,L,S,G]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['triangle lamina', [['mvfs', 'mev', 'mev', 'mef']], [3, 3, 2, 2, 1, 0]], ['tetrahedron', [['mvfs', 'mev', 'mev', 'mef', 'mev', 'mef', 'mef']], [4, 6, 4, 4, 1, 0]], ['square with hole ring', [['mvfs', 'mev', 'mev', 'mev', 'mef', 'mev', 'mev', 'mev', 'mef', 'kemr']], [7, 7, 3, 4, 1, 0]], ['torus handle', [['mvfs', 'mev', 'mev', 'mev', 'mef', 'mev', 'mev', 'mev', 'mef', 'kemr', 'kfmrh']], [7, 7, 2, 4, 1, 1]], ['undo handle', [['mvfs', 'mev', 'mev', 'mev', 'mef', 'mev', 'mev', 'mev', 'mef', 'kemr', 'kfmrh', 'mfkrh']], [7, 7, 3, 4, 1, 0]], ['ring then remake edge', [['mvfs', 'mev', 'mev', 'mef', 'mev', 'kemr', 'mekr']], [4, 4, 2, 2, 1, 0]], ['loop deficit', [['mvfs', 'mev', 'mekr']], ['invalid', 2]]], [['torus handle', [['mvfs', 'mev', 'mev', 'mev', 'mef', 'mev', 'mev', 'mev', 'mef', 'kemr', 'kfmrh']], [7, 7, 2, 4, 1, 1]], ['undo handle', [['mvfs', 'mev', 'mev', 'mev', 'mef', 'mev', 'mev', 'mev', 'mef', 'kemr', 'kfmrh', 'mfkrh']], [7, 7, 3, 4, 1, 0]], ['ring then remake edge', [['mvfs', 'mev', 'mev', 'mef', 'mev', 'kemr', 'mekr']], [4, 4, 2, 2, 1, 0]], ['kill edge on empty', [['mvfs', 'kev']], ['invalid', 1]], ['unknown op', [['mvfs', 'mev', 'split']], ['unknown', 2]], ['uppercase op', [['mvfs', 'MEV']], ['unknown', 1]], ['loop deficit', [['mvfs', 'mev', 'mekr']], ['invalid', 2]]], [['kill edge on empty', [['mvfs', 'kev']], ['invalid', 1]], ['unknown op', [['mvfs', 'mev', 'split']], ['unknown', 2]], ['uppercase op', [['mvfs', 'MEV']], ['unknown', 1]], ['loop deficit', [['mvfs', 'mev', 'mekr']], ['invalid', 2]], ['two shells', [['mvfs', 'mev', 'mvfs', 'mev', 'mev', 'mef']], [5, 4, 3, 3, 2, 0]], ['face without loop', [['mvfs', 'mfkrh']], ['invalid', 1]], ['build and kill', [['mvfs', 'mev', 'mev', 'mef', 'kef', 'kev', 'kev', 'kvfs']], [0, 0, 0, 0, 0, 0]]], [['triangle lamina', [['mvfs', 'mev', 'mev', 'mef']], [3, 3, 2, 2, 1, 0]], ['tetrahedron', [['mvfs', 'mev', 'mev', 'mef', 'mev', 'mef', 'mef']], [4, 6, 4, 4, 1, 0]], ['loop deficit', [['mvfs', 'mev', 'mekr']], ['invalid', 2]], ['two shells', [['mvfs', 'mev', 'mvfs', 'mev', 'mev', 'mef']], [5, 4, 3, 3, 2, 0]], ['face without loop', [['mvfs', 'mfkrh']], ['invalid', 1]], ['build and kill', [['mvfs', 'mev', 'mev', 'mef', 'kef', 'kev', 'kev', 'kvfs']], [0, 0, 0, 0, 0, 0]], ['hole into lamina', [['mvfs', 'mev', 'mev', 'mef', 'mev', 'mev', 'mev', 'mef', 'kemr', 'kfmrh', 'mev']], [7, 7, 2, 4, 1, 1]]], [['triangle lamina', [['mvfs', 'mev', 'mev', 'mef']], [3, 3, 2, 2, 1, 0]], ['tetrahedron', [['mvfs', 'mev', 'mev', 'mef', 'mev', 'mef', 'mef']], [4, 6, 4, 4, 1, 0]], ['square with hole ring', [['mvfs', 'mev', 'mev', 'mev', 'mef', 'mev', 'mev', 'mev', 'mef', 'kemr']], [7, 7, 3, 4, 1, 0]], ['torus handle', [['mvfs', 'mev', 'mev', 'mev', 'mef', 'mev', 'mev', 'mev', 'mef', 'kemr', 'kfmrh']], [7, 7, 2, 4, 1, 1]], ['undo handle', [['mvfs', 'mev', 'mev', 'mev', 'mef', 'mev', 'mev', 'mev', 'mef', 'kemr', 'kfmrh', 'mfkrh']], [7, 7, 3, 4, 1, 0]], ['loop deficit', [['mvfs', 'mev', 'mekr']], ['invalid', 2]], ['hole into lamina', [['mvfs', 'mev', 'mev', 'mef', 'mev', 'mev', 'mev', 'mef', 'kemr', 'kfmrh', 'mev']], [7, 7, 2, 4, 1, 1]]]]
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
triangle lamina[3, 3, 2, 2, 1, 0][3, 3, 2, 2, 1, 0]Passed
tetrahedron[4, 6, 4, 4, 1, 0][4, 6, 4, 4, 1, 0]Passed
square with hole ring[7, 7, 3, 4, 1, 0][7, 7, 3, 4, 1, 0]Passed
torus handle[7, 7, 2, 4, 1, 1][7, 7, 2, 4, 1, 1]Passed
undo handle[7, 7, 3, 4, 1, 0][7, 7, 3, 4, 1, 0]Passed
ring then remake edge[4, 4, 2, 2, 1, 0][4, 4, 2, 2, 1, 0]Passed
loop deficit[2, 2, 1, 0, 1, 0]['invalid', 2]Failed

SHA-256 / d41ec8178985342d8746732365d11acb6168b500b67ebaaea316edb08e359412

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 7 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

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Verification & scope

Pure combinatorial teaching model over integer face lists with a stipulated contract; no geometry kernel or file format is implied. 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 2026-09-29T14:51:10.724686+00:00.

Case digest / c5de3e7dcbb49fc359c72401a1ce8a2989ae47e6087bc76d96b9fd13a0f985c2