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In set theory, a universal set is a set which contains all objects, including itself. [1] ... it would necessarily be a subset of the set of all sets, provided that ...
A is a subset of B (denoted ) and, conversely, B is a superset of A (denoted ). In mathematics, a set A is a subset of a set B if all elements of A are also elements of B; B is then a superset of A. It is possible for A and B to be equal; if they are unequal, then A is a proper subset of B.
However, once subsets of a given set X (in Cantor's case, X = R) are considered, the universe may need to be a set of subsets of X. (For example, a topology on X is a set of subsets of X.) The various sets of subsets of X will not themselves be subsets of X but will instead be subsets of PX, the power set of X.
For instance, when investigating properties of the real numbers R (and subsets of R), R may be taken as the universal set. A true universal set is not included in standard set theory (see Paradoxes below), but is included in some non-standard set theories. Given a universal set U and a subset A of U, the complement of A (in U) is defined as
For example, {1, 2} is a subset of {1, 2, 3}, and so is {2} but {1, 4} is not. As implied by this definition, a set is a subset of itself. For cases where this possibility is unsuitable or would make sense to be rejected, the term proper subset is defined. A is called a proper subset of B if and only if A is a subset of B, but A is not equal to B.
A set of polygons in an Euler diagram This set equals the one depicted above since both have the very same elements.. In mathematics, a set is a collection of different [1] things; [2] [3] [4] these things are called elements or members of the set and are typically mathematical objects of any kind: numbers, symbols, points in space, lines, other geometrical shapes, variables, or even other ...
may mean that A is a subset of B, and is possibly equal to B; that is, every element of A belongs to B; expressed as a formula, ,. 2. A ⊂ B {\displaystyle A\subset B} may mean that A is a proper subset of B , that is the two sets are different, and every element of A belongs to B ; expressed as a formula, A ≠ B ∧ ∀ x , x ∈ A ⇒ x ∈ ...
geometry corresponds to an experimental reality geometry is a mathematical truth all geometric properties of the space follow from the axioms axioms of a space need not determine all geometric properties geometry is an autonomous and living science classical geometry is a universal language of mathematics space is three-dimensional