Math 2.0

Mathematical logic and foundations Definition

Element

Definition

Let AA be a set and let xx be an object. The object xx is an element of AA, written x∈Ax \in A, when AA contains xx. Otherwise, xx is not an element of AA, written x∉Ax \notin A. The proposition x∉Ax \notin A is the negation of x∈Ax \in A.

Remarks

Other phrases for x∈Ax \in A are "xx is a member of AA", "xx belongs to AA" and "xx is in AA". For A={1,2,3}A = \{1, 2, 3\}, 2∈A2 \in A and 4∉A4 \notin A. An element of a set can itself be a set: {1}∈{{1},2}\{1\} \in \{\{1\}, 2\}, but 1∉{{1},2}1 \notin \{\{1\}, 2\}.

Where this leads

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Further reading

  1. Web https://en.wikipedia.org/wiki/Element_of_a_set, lead section
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