"empty function" meaning in English

{
  "forms": [
    {
      "form": "empty functions",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "empty function (plural empty functions)",
      "name": "en-noun"
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  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
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          "langcode": "en",
          "name": "Mathematics",
          "orig": "en:Mathematics",
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            "Formal sciences",
            "Sciences",
            "All topics",
            "Fundamental"
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          "source": "w"
        }
      ],
      "glosses": [
        "A function whose domain is the empty set."
      ],
      "hypernyms": [
        {
          "word": "function"
        }
      ],
      "id": "en-empty_function-en-noun-Ct6zANQd",
      "links": [
        [
          "mathematics",
          "mathematics"
        ],
        [
          "function",
          "function"
        ],
        [
          "domain",
          "domain"
        ],
        [
          "empty set",
          "empty set"
        ]
      ],
      "raw_glosses": [
        "(mathematics) A function whose domain is the empty set."
      ],
      "topics": [
        "mathematics",
        "sciences"
      ],
      "wikipedia": [
        "empty function"
      ]
    }
  ],
  "word": "empty function"
}

{
  "forms": [
    {
      "form": "empty functions",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "empty function (plural empty functions)",
      "name": "en-noun"
    }
  ],
  "hypernyms": [
    {
      "word": "function"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
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        "English multiword terms",
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      "glosses": [
        "A function whose domain is the empty set."
      ],
      "links": [
        [
          "mathematics",
          "mathematics"
        ],
        [
          "function",
          "function"
        ],
        [
          "domain",
          "domain"
        ],
        [
          "empty set",
          "empty set"
        ]
      ],
      "raw_glosses": [
        "(mathematics) A function whose domain is the empty set."
      ],
      "topics": [
        "mathematics",
        "sciences"
      ],
      "wikipedia": [
        "empty function"
      ]
    }
  ],
  "word": "empty function"
}