Math 2.0

definition

Universal set

Definition

In a given context, fix a set UU such that all the sets under discussion are subsets of UU. The set UU is then the universal set, or the universe of discourse, of the context.

Remarks

In elementary number theory, UU can be the set Z\mathbb{Z} of integers. The complement of a set is taken relative to the universal set. In Zermelo–Fraenkel set theory, no set contains all sets. This is a consequence of Russell's paradox.

Explanations

L1 human

The universal set is the "whole world" of a problem. In a problem about real numbers, it is R\mathbb{R}. In a Venn diagram, it is the rectangle that contains all the circles.

What this node needs for W2
  • edge instance_of in: one example (0 of 1)
  • edge not_instance_of in: one non-example that fails one clause (0 of 1)

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What depends on this

236 nodes use this node, directly or through other nodes.

Sources

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