Math 2.0

Mathematical logic and foundations Definition

Union

Builds on SetElementDisjunction

Definition

Let AA and BB be sets. The union of AA and BB is the set A∪B={x∣x∈A∨x∈B}.A \cup B = \{x \mid x \in A \lor x \in B\}. So an object xx is an element of A∪BA \cup B when x∈Ax \in A or x∈Bx \in B, or both.

Remarks

Example: {1,2}∪{2,3}={1,2,3}\{1, 2\} \cup \{2, 3\} = \{1, 2, 3\}. Union is commutative and associative, and A∪∅=AA \cup \varnothing = A. The union of an arbitrary family of sets is in union of a family of sets.

Reading path

To understand this page from the ground up, read these 5 pages in order. The foundations come first.

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Each page uses the pages above it. The colour of the bar on a box shows how strong the evidence is, and the box also gives it as text. The list has the same pages.
  • no evidence level
  1. Element definition
  2. Proposition concept
  3. Set definition
  4. Disjunction definition
  5. Union definition

Where this leads

745 pages build on this one.

Further reading

  1. Web https://en.wikipedia.org/wiki/Union_(set_theory), lead section
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DefinesUnion
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