The set of cars with 20 doors. There are some sets that do not contain any element at all.

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The Null set or Empty set. We call a set with no elements the null or empty set. For example, the set of months with 32 days. We can write out the two sets: 1. Some other example of null sets are: The set of dogs with six legs. From OeisWiki. [math]\{\emptyset\} = \{\{\}\}[/math]. The set of squares with 5 sides. It is represented by the symbol { } or Ø . List of LaTeX mathematical symbols.
Encuentra aquí el comando y paquete que necesitas para escribir el símbolo de conjunto vacío en LaTeX. [math]\emptyset = \{\};[/math] 2. We've documented and categorized hundreds of macros! No installation, real-time collaboration, version control, hundreds of LaTeX templates, and more.

... Set and/or logic notation.