"Kirkman's schoolgirl problem" meaning in English

{
  "etymology_text": "Proposed by Rev. Thomas Penyngton Kirkman in 1850.",
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      "expansion": "Kirkman's schoolgirl problem",
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  "lang_code": "en",
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      "glosses": [
        "A problem in combinatorics, in which 15 schoolgirls go walking three abreast for seven days in succession, and must be arranged so that no two walk abreast more than once."
      ],
      "id": "en-Kirkman's_schoolgirl_problem-en-name-UunhL1WO",
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          "combinatorics",
          "combinatorics"
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        [
          "abreast",
          "abreast"
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      "raw_glosses": [
        "(mathematics) A problem in combinatorics, in which 15 schoolgirls go walking three abreast for seven days in succession, and must be arranged so that no two walk abreast more than once."
      ],
      "topics": [
        "mathematics",
        "sciences"
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    }
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  "word": "Kirkman's schoolgirl problem"
}

{
  "etymology_text": "Proposed by Rev. Thomas Penyngton Kirkman in 1850.",
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      "expansion": "Kirkman's schoolgirl problem",
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  "lang_code": "en",
  "pos": "name",
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      "glosses": [
        "A problem in combinatorics, in which 15 schoolgirls go walking three abreast for seven days in succession, and must be arranged so that no two walk abreast more than once."
      ],
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          "mathematics",
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          "combinatorics"
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        [
          "abreast",
          "abreast"
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      ],
      "raw_glosses": [
        "(mathematics) A problem in combinatorics, in which 15 schoolgirls go walking three abreast for seven days in succession, and must be arranged so that no two walk abreast more than once."
      ],
      "topics": [
        "mathematics",
        "sciences"
      ]
    }
  ],
  "word": "Kirkman's schoolgirl problem"
}