"σ-additivity" meaning in English

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      "expansion": "σ-additivity (uncountable)",
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  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
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          "kind": "topical",
          "langcode": "en",
          "name": "Mathematical analysis",
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            "Formal sciences",
            "Sciences",
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          "kind": "topical",
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          "name": "Measure theory",
          "orig": "en:Measure theory",
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            "Formal sciences",
            "Sciences",
            "All topics",
            "Fundamental"
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      ],
      "glosses": [
        "countable additivity"
      ],
      "id": "en-σ-additivity-en-noun-GEDrsnN9",
      "links": [
        [
          "mathematical analysis",
          "mathematical analysis"
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        [
          "countable additivity",
          "countable additivity"
        ]
      ],
      "raw_glosses": [
        "(mathematical analysis) countable additivity"
      ],
      "synonyms": [
        {
          "word": "sigma additivity"
        }
      ],
      "tags": [
        "uncountable"
      ],
      "topics": [
        "mathematical-analysis",
        "mathematics",
        "sciences"
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      "translations": [
        {
          "code": "de",
          "lang": "German",
          "sense": "Translations",
          "tags": [
            "feminine"
          ],
          "word": "σ-Additivität"
        },
        {
          "code": "ru",
          "lang": "Russian",
          "roman": "σ-additivnostʹ",
          "sense": "Translations",
          "tags": [
            "feminine"
          ],
          "word": "σ-аддитивность"
        }
      ],
      "wikipedia": [
        "sigma additivity"
      ]
    }
  ],
  "word": "σ-additivity"
}

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  "lang_code": "en",
  "pos": "noun",
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      "glosses": [
        "countable additivity"
      ],
      "links": [
        [
          "mathematical analysis",
          "mathematical analysis"
        ],
        [
          "countable additivity",
          "countable additivity"
        ]
      ],
      "raw_glosses": [
        "(mathematical analysis) countable additivity"
      ],
      "tags": [
        "uncountable"
      ],
      "topics": [
        "mathematical-analysis",
        "mathematics",
        "sciences"
      ],
      "wikipedia": [
        "sigma additivity"
      ]
    }
  ],
  "synonyms": [
    {
      "word": "sigma additivity"
    }
  ],
  "translations": [
    {
      "code": "de",
      "lang": "German",
      "sense": "Translations",
      "tags": [
        "feminine"
      ],
      "word": "σ-Additivität"
    },
    {
      "code": "ru",
      "lang": "Russian",
      "roman": "σ-additivnostʹ",
      "sense": "Translations",
      "tags": [
        "feminine"
      ],
      "word": "σ-аддитивность"
    }
  ],
  "word": "σ-additivity"
}