"Fσ" meaning in All languages combined

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        "3": "fermé",
        "4": "",
        "5": "closed"
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      "expansion": "French fermé (“closed”)",
      "name": "der"
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      "args": {
        "1": "fr",
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        "3": "",
        "4": "sum"
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      "expansion": "somme (“sum”)",
      "name": "m"
    }
  ],
  "etymology_text": "From French fermé (“closed”) for the 'F' and French somme (“sum”) for the 'σ'. The 'σ' can be interpreted to mean \"countable union.\"",
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    {
      "form": "F_σ",
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  "lang_code": "mul",
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          "name": "Mathematical analysis",
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            "Mathematics",
            "Formal sciences",
            "Sciences",
            "All topics",
            "Fundamental"
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        },
        {
          "kind": "topical",
          "langcode": "mul",
          "name": "Measure theory",
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            "Mathematics",
            "Formal sciences",
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          "name": "Topology",
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        }
      ],
      "glosses": [
        "A countable union of closed sets."
      ],
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        {
          "word": "Borel set"
        }
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      "id": "en-Fσ-mul-symbol-Xsv4uoi1",
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        [
          "mathematical analysis",
          "mathematical analysis"
        ],
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          "topology",
          "topology"
        ],
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          "countable",
          "countable"
        ],
        [
          "union",
          "union"
        ],
        [
          "closed set",
          "closed set"
        ]
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        "(mathematical analysis, topology) A countable union of closed sets."
      ],
      "topics": [
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        "sciences",
        "topology"
      ],
      "wikipedia": [
        "Fσ set"
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      "name": "der"
    },
    {
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        "2": "somme",
        "3": "",
        "4": "sum"
      },
      "expansion": "somme (“sum”)",
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  ],
  "etymology_text": "From French fermé (“closed”) for the 'F' and French somme (“sum”) for the 'σ'. The 'σ' can be interpreted to mean \"countable union.\"",
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    {
      "form": "F_σ",
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  ],
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  ],
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  "pos": "symbol",
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        [
          "mathematical analysis",
          "mathematical analysis"
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          "topology"
        ],
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      ],
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