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Set Theory Basics
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Subset
A set where all its elements are contained within another set. Notation: .
Union of sets
The set of all distinct elements that are in either set. Notation: .
Set difference
The set of elements that are in one set but not in the other. Notation: or .
Symmetric difference
The set of elements which are in either of the sets and not in their intersection. Notation: .
Codomain of a function
The set that contains all possible outputs of a function. Notation: If , then is the codomain.
One-to-one function (Injective)
A function where each element of the range is mapped to by exactly one element of the domain. Notation: is injective if implies .
Cardinality of a set
The number of elements in a set. Notation: or .
Empty set
A set with no elements. Notation: or .
Complement of a set
The set of all elements in the universal set that are not in the given set. Notation: or .
Partition of a set
A division of a set into non-overlapping subsets that cover all elements of the original set.
Universal set
The set that contains all objects or elements under consideration. Notation: Usually denoted by or .
Disjoint sets
Two sets with no common elements. Notation: .
Equivalence relation
A relation that is reflexive, symmetric, and transitive. Notation: indicates is equivalent to .
Well-defined function
A function where the output value is uniquely determined by the input, adhering to the definition of a function.
Ordered pair
A pair of elements with an order, where the first element is considered the first component of the pair. Notation: .
Domain of a function
The set of all possible inputs for which the function is defined. Notation: If , then is the domain.
Power set
The set of all subsets of a set, including the empty set and the set itself. Notation: or .
Cartesian product of sets
The set of all ordered pairs obtained by the product of two sets. Notation: .
Function (mapping)
A relation between sets that associates each element of a set with exactly one element of another set. Notation: .
Bijection (Bijective function)
A function that is both injective and surjective, meaning it is a one-to-one correspondence between the domain and codomain. Notation: is bijective if it is both one-to-one and onto.
Inverse of a function
A function that reverses the direction of a given function, if such a function exists. Notation: for the inverse of .
Onto function (Surjective)
A function where each element of the codomain is the image of at least one element of the domain. Notation: is surjective if for every in the codomain, there is an in the domain such that .
Intersection of sets
The set of elements that are common to both sets. Notation: .
Proper subset
A subset that is not equal to the parent set. Notation: .
Image of a function
The set of all outputs that the function actually produces. Notation: If and is a subset of , then is the image of .
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