Injective function

In mathematics, an injective function (also known as injection, or one-to-one function[1] ) is a function f that maps distinct elements of its domain to distinct elements of its codomain; that is, x1x2 implies f(x1) ≠ f(x2) (equivalently by contraposition, f(x1) = f(x2) implies x1 = x2). In other words, every element of the function's codomain is the image of at most one element of its domain.[2] The term one-to-one function must not be confused with one-to-one correspondence that refers to bijective functions, which are functions such that each element in the codomain is an image of exactly one element in the domain.

A homomorphism between algebraic structures is a function that is compatible with the operations of the structures. For all common algebraic structures, and, in particular for vector spaces, an injective homomorphism is also called a monomorphism. However, in the more general context of category theory, the definition of a monomorphism differs from that of an injective homomorphism.[3] This is thus a theorem that they are equivalent for algebraic structures; see Homomorphism § Monomorphism for more details.

A function that is not injective is sometimes called many-to-one.[2]

  1. ^ Sometimes one-one function, in Indian mathematical education. "Chapter 1:Relations and functions" (PDF). Archived (PDF) from the original on Dec 26, 2023 – via NCERT.
  2. ^ a b "Injective, Surjective and Bijective". Math is Fun. Retrieved 2019-12-07.
  3. ^ "Section 7.3 (00V5): Injective and surjective maps of presheaves". The Stacks project. Retrieved 2019-12-07.

Injective function

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