"in book" meaning in English

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  "head_templates": [
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      "args": {
        "1": "en",
        "2": "prepositional phrase"
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      "expansion": "in book",
      "name": "head"
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  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "prep_phrase",
  "senses": [
    {
      "antonyms": [
        {
          "word": "out of book"
        }
      ],
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
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          "source": "w"
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          "source": "w"
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          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Chess",
          "orig": "en:Chess",
          "parents": [
            "Board games",
            "Tabletop games",
            "Games",
            "Recreation",
            "Human activity",
            "Human behaviour",
            "Human",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
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      "examples": [
        {
          "ref": "2022 January 21, Colin McGourty, “Tata Steel 5: Rapport & Mamedyarov hit the front”, in chess24, archived from the original on 2022-05-19:",
          "text": "The Sicilian opening was wild, but the speed of play made it clear both players were \"in book\", up to a point.",
          "type": "quote"
        },
        {
          "ref": "2023 January 19, Mark Crowther, “Giri overtakes Abdusattorov in a dramatic final round of the Tata Steel Masters to grab his first title”, in The Week in Chess, archived from the original on 2023-02-01:",
          "text": "Wesley So had prepared a line with a temporary pawn sacrifice against Praggnanandhaa and both players appeared to be in book for a long time.",
          "type": "quote"
        }
      ],
      "glosses": [
        "Of a chess player: following a main line (\"a standard sequence of opening moves considered to be best play\")."
      ],
      "id": "en-in_book-en-prep_phrase-lKSIrTvX",
      "links": [
        [
          "chess",
          "chess"
        ],
        [
          "player",
          "player"
        ],
        [
          "main line",
          "main line"
        ]
      ],
      "raw_glosses": [
        "(chess, uncommon) Of a chess player: following a main line (\"a standard sequence of opening moves considered to be best play\")."
      ],
      "tags": [
        "uncommon"
      ],
      "topics": [
        "board-games",
        "chess",
        "games"
      ]
    }
  ],
  "word": "in book"
}

{
  "head_templates": [
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        "2": "prepositional phrase"
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      "expansion": "in book",
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  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "prep_phrase",
  "senses": [
    {
      "antonyms": [
        {
          "word": "out of book"
        }
      ],
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        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English prepositional phrases",
        "English terms with quotations",
        "English terms with uncommon senses",
        "Pages with 1 entry",
        "Pages with entries",
        "en:Chess"
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      "examples": [
        {
          "ref": "2022 January 21, Colin McGourty, “Tata Steel 5: Rapport & Mamedyarov hit the front”, in chess24, archived from the original on 2022-05-19:",
          "text": "The Sicilian opening was wild, but the speed of play made it clear both players were \"in book\", up to a point.",
          "type": "quote"
        },
        {
          "ref": "2023 January 19, Mark Crowther, “Giri overtakes Abdusattorov in a dramatic final round of the Tata Steel Masters to grab his first title”, in The Week in Chess, archived from the original on 2023-02-01:",
          "text": "Wesley So had prepared a line with a temporary pawn sacrifice against Praggnanandhaa and both players appeared to be in book for a long time.",
          "type": "quote"
        }
      ],
      "glosses": [
        "Of a chess player: following a main line (\"a standard sequence of opening moves considered to be best play\")."
      ],
      "links": [
        [
          "chess",
          "chess"
        ],
        [
          "player",
          "player"
        ],
        [
          "main line",
          "main line"
        ]
      ],
      "raw_glosses": [
        "(chess, uncommon) Of a chess player: following a main line (\"a standard sequence of opening moves considered to be best play\")."
      ],
      "tags": [
        "uncommon"
      ],
      "topics": [
        "board-games",
        "chess",
        "games"
      ]
    }
  ],
  "word": "in book"
}