FA-98196 / Attention mask construction / Open access
Global tokens are incorrectly limited by local window · case 01
Global tokens are incorrectly limited by local window.
ROOT CAUSE
A uniform sliding window ignores explicitly global key positions.
THE FAILURE
A uniform sliding window ignores explicitly global key positions.
Unsuccessful approach: Shrinking the local window by one underfills ordinary rows even after global keys are admitted.
Case contract
Causal local window W; any listed global key <= query is visible at any distance.
Why this case matters
A small explicit visibility matrix makes sequence-attention boundary behavior reviewable.
1 / The failure
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(length, window, global_keys):
return [[window>0 and 0<=i-j<window for j in range(length)] for i in range(length)]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
g=[0]
check('old global key',solve(N+2,2,g),[[j<=i and (j in g or (2>0 and i-j<2)) for j in range(N+2)] for i in range(N+2)])
check('no globals',solve(3,2,[]),[[j<=i and i-j<2 for j in range(3)] for i in range(3)])
check('global future still hidden',solve(3,1,[2])[0],[True,False,False])
check('zero window global only',solve(3,0,[0]),[[j==0 and j<=i for j in range(3)] for i in range(3)])
check('empty sequence',solve(0,2,[]),[])
check('global old key at last row',solve(4,1,[0])[3],[True,False,False,True])
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 |
|---|---|---|---|
| old global key | [[True, False, False], [True, True, False], [False, True, True]] | [[True, False, False], [True, True, False], [True, True, True]] | Failed |
| no globals | [[True, False, False], [True, True, False], [False, True, True]] | [[True, False, False], [True, True, False], [False, True, True]] | Passed |
| global future still hidden | [True, False, False] | [True, False, False] | Passed |
| zero window global only | [[False, False, False], [False, False, False], [False, False, False]] | [[True, False, False], [True, False, False], [True, False, False]] | Failed |
| empty sequence | [] | [] | Passed |
| global old key at last row | [False, False, False, True] | [True, False, False, True] | Failed |
SHA-256 / adbb996f0389cad51c6f1e84bb969458c95b49dd0d04f254afdbda11ff892481
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(length, window, global_keys):
return [[j<=i and (j in global_keys or i-j<window-1) for j in range(length)] for i in range(length)]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
g=[0]
check('old global key',solve(N+2,2,g),[[j<=i and (j in g or (2>0 and i-j<2)) for j in range(N+2)] for i in range(N+2)])
check('no globals',solve(3,2,[]),[[j<=i and i-j<2 for j in range(3)] for i in range(3)])
check('global future still hidden',solve(3,1,[2])[0],[True,False,False])
check('zero window global only',solve(3,0,[0]),[[j==0 and j<=i for j in range(3)] for i in range(3)])
check('empty sequence',solve(0,2,[]),[])
check('global old key at last row',solve(4,1,[0])[3],[True,False,False,True])
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 |
|---|---|---|---|
| old global key | [[True, False, False], [True, True, False], [True, False, True]] | [[True, False, False], [True, True, False], [True, True, True]] | Failed |
| no globals | [[True, False, False], [False, True, False], [False, False, True]] | [[True, False, False], [True, True, False], [False, True, True]] | Failed |
| global future still hidden | [False, False, False] | [True, False, False] | Failed |
| zero window global only | [[True, False, False], [True, False, False], [True, False, False]] | [[True, False, False], [True, False, False], [True, False, False]] | Passed |
| empty sequence | [] | [] | Passed |
| global old key at last row | [True, False, False, False] | [True, False, False, True] | Failed |
SHA-256 / c6fe4cd3455e3dbf49bbcee32f8fd09fb4655c28451d73110b5ff39c729b487d
HELD IN THE MEMBER ARCHIVE
The verified repair and its recorded checks are member-only.
This mechanism has 6 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.
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Sign in to the archive ↗Verification & scope
These are toy Boolean matrix contracts; they do not define a production model architecture or tensor library behavior. 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 2026-09-30T16:48:10.194056+00:00.
Case digest / cbc6ac208fd92a8f907aab6c209228744d91757e7090cff858baf31c824f2d08