Math 2.0

statement theorem

Distributive laws for sets

Statement

Let AA, BB and CC be sets. Then intersection distributes over union, and union distributes over intersection: A∩(B∪C)=(A∩B)∪(A∩C),A \cap (B \cup C) = (A \cap B) \cup (A \cap C), A∪(B∩C)=(A∪B)∩(A∪C).A \cup (B \cap C) = (A \cup B) \cap (A \cup C).

Remarks

The laws follow from the distributive laws of logic for ∧\land and ∨\lor. The second law has no analogue for numbers: a+bca + bc is not (a+b)(a+c)(a + b)(a + c) in general.

Explanations

L1 human

To prove the first law, take xx in the left side. Then x∈Ax \in A, and x∈Bx \in B or x∈Cx \in C. In the first case x∈A∩Bx \in A \cap B, and in the second case x∈A∩Cx \in A \cap C. The other inclusion is similar.

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Sources

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