{"abstract":"The operation returns a result or retained state that violates this contract: Retain all left occurrences with no equal value in right.","category":"Collection algebra","checks":5,"contract":"Retain all left occurrences with no equal value in right. Inputs are the finite Python values shown by the executable fixtures; no concurrent execution is assumed.","contract_signature":"x, y=None","evaluation_group":"model-5f7eed35dc54642c","failed_approach":"Swapping operands emits unmatched right values instead.","family":"xr-left-filter-difference-keeps-occurrences","id":"FA-4256","implementations":{"attempt":{"sha256":"8d4b6f4289ce7974f038cb546b0b1af8683de0c785ae92c42939c5e58781f03f","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return [v for v in y if v not in x]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('both empty', solve([], []), [])\ncheck('empty right operand', solve(['a'], []), ['a'])\ncheck('empty left operand', solve([], ['b']), [])\ncheck('overlap and multiplicity', solve(['b', 'a', 'b'], ['b', 'c', 'c']), ['a'])\ncheck('unmatched duplicate remains', solve(['a','a'], []), ['a','a'])\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":"8e427b18c21a61a788ee83bae89aca49cd0e933f387742bf95d6c9baf8c84cd0","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return [v for v in dict.fromkeys(x) if v not in y]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('both empty', solve([], []), [])\ncheck('empty right operand', solve(['a'], []), ['a'])\ncheck('empty left operand', solve([], ['b']), [])\ncheck('overlap and multiplicity', solve(['b', 'a', 'b'], ['b', 'c', 'c']), ['a'])\ncheck('unmatched duplicate remains', solve(['a','a'], []), ['a','a'])\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":" 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":"xr-left-filter-difference-keeps-occurrences","generated_at":"2026-09-29T14:37:37.189477+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"A controlled local-runtime regression for collection APIs, language semantics, or ownership wrappers. Fixtures include boundary and interaction cases.","root_cause":"Distinct-value conversion removes repeated unmatched left occurrences.","sha256":"458a484a5b2b1f4f89499757717189221098e03ff6a825889b6a59036b424029","title":"Left filter difference keeps occurrences · case 01","variant":1,"variant_policy":"Five execution reruns of a fixed adversarial fixture suite; variant number does not alter semantic inputs.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":35.743,"exit_code":1,"observations":[{"actual":[],"check":"both empty","expected":[],"passed":true},{"actual":[],"check":"empty right operand","expected":["a"],"passed":false},{"actual":["b"],"check":"empty left operand","expected":[],"passed":false},{"actual":["c","c"],"check":"overlap and multiplicity","expected":["a"],"passed":false},{"actual":[],"check":"unmatched duplicate remains","expected":["a","a"],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"both empty\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"empty right operand\", \"actual\": [], \"expected\": [\"a\"], \"passed\": false}, {\"check\": \"empty left operand\", \"actual\": [\"b\"], \"expected\": [], \"passed\": false}, {\"check\": \"overlap and multiplicity\", \"actual\": [\"c\", \"c\"], \"expected\": [\"a\"], \"passed\": false}, {\"check\": \"unmatched duplicate remains\", \"actual\": [], \"expected\": [\"a\", \"a\"], \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":40.569,"exit_code":1,"observations":[{"actual":[],"check":"both empty","expected":[],"passed":true},{"actual":["a"],"check":"empty right operand","expected":["a"],"passed":true},{"actual":[],"check":"empty left operand","expected":[],"passed":true},{"actual":["a"],"check":"overlap and multiplicity","expected":["a"],"passed":true},{"actual":["a"],"check":"unmatched duplicate remains","expected":["a","a"],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"both empty\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"empty right operand\", \"actual\": [\"a\"], \"expected\": [\"a\"], \"passed\": true}, {\"check\": \"empty left operand\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"overlap and multiplicity\", \"actual\": [\"a\"], \"expected\": [\"a\"], \"passed\": true}, {\"check\": \"unmatched duplicate remains\", \"actual\": [\"a\"], \"expected\": [\"a\", \"a\"], \"passed\": false}], \"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."}}