{"abstract":"The operation returns a result or retained state that violates this contract: Retain every left occurrence whose value occurs anywhere in right.","category":"Collection algebra","checks":4,"contract":"Retain every left occurrence whose value occurs anywhere in right. Inputs are the finite Python values shown by the executable fixtures; no concurrent execution is assumed.","evaluation_group":"model-46d292d4ce16a2f3","failed_approach":"Returning matching right values changes the source multiplicity.","family":"xr-left-semijoin-preserves-left-duplicates","id":"FA-4246","implementations":{"attempt":{"sha256":"193167f68055aaa6bba30548b9038599470a15fd59abe399f01a83c5ffa61352","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 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'], []), [])\ncheck('empty left operand', solve([], ['b']), [])\ncheck('overlap and multiplicity', solve(['b', 'a', 'b'], ['b', 'c', 'c']), ['b', 'b'])\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":"ca52e0391a3e98bbba2cc399cde21fc4bd06c5c0f09667f87d4786d5e4785e7a","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return list(dict.fromkeys(v for v in x if v 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'], []), [])\ncheck('empty left operand', solve([], ['b']), [])\ncheck('overlap and multiplicity', solve(['b', 'a', 'b'], ['b', 'c', 'c']), ['b', 'b'])\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"},"fixed":{"sha256":"aca288e46645dbce2cff34a3188b7b19bb15038797a64d0890fd88d8c751d509","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 x if v 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'], []), [])\ncheck('empty left operand', solve([], ['b']), [])\ncheck('overlap and multiplicity', solve(['b', 'a', 'b'], ['b', 'c', 'c']), ['b', 'b'])\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-semijoin-preserves-left-duplicates","generated_at":"2026-09-29T14:37:37.182249+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.","repair":"Retain every left occurrence whose value occurs anywhere in right.","root_cause":"Distinct-value conversion discards repeated matching left occurrences.","sha256":"aa20f7a7f5262fcc8a79930bcdc7ae6027ac462eb7739ddc79cd20b34cfc9ef7","title":"Left semijoin preserves left duplicates · case 01","variant":1,"variant_policy":"Five execution reruns of a fixed adversarial fixture suite; variant number does not alter semantic inputs.","verification":{"attempt":{"elapsed_ms":38.241,"exit_code":1,"observations":[{"actual":[],"check":"both empty","expected":[],"passed":true},{"actual":[],"check":"empty right operand","expected":[],"passed":true},{"actual":[],"check":"empty left operand","expected":[],"passed":true},{"actual":["b"],"check":"overlap and multiplicity","expected":["b","b"],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"both empty\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"empty right operand\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"empty left operand\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"overlap and multiplicity\", \"actual\": [\"b\"], \"expected\": [\"b\", \"b\"], \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":38.983,"exit_code":1,"observations":[{"actual":[],"check":"both empty","expected":[],"passed":true},{"actual":[],"check":"empty right operand","expected":[],"passed":true},{"actual":[],"check":"empty left operand","expected":[],"passed":true},{"actual":["b"],"check":"overlap and multiplicity","expected":["b","b"],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"both empty\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"empty right operand\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"empty left operand\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"overlap and multiplicity\", \"actual\": [\"b\"], \"expected\": [\"b\", \"b\"], \"passed\": false}], \"passed\": false}\n"},"fixed":{"elapsed_ms":37.255,"exit_code":0,"observations":[{"actual":[],"check":"both empty","expected":[],"passed":true},{"actual":[],"check":"empty right operand","expected":[],"passed":true},{"actual":[],"check":"empty left operand","expected":[],"passed":true},{"actual":["b","b"],"check":"overlap and multiplicity","expected":["b","b"],"passed":true}],"passed":true,"stderr":"","stdout":"{\"observations\": [{\"check\": \"both empty\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"empty right operand\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"empty left operand\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"overlap and multiplicity\", \"actual\": [\"b\", \"b\"], \"expected\": [\"b\", \"b\"], \"passed\": true}], \"passed\": true}\n"}},"verified":true,"visibility":"public"}