👉 In mathematics, a function f from a set X to a set Y is called surjective if for every element y in Y there exists an element x in X such that f(x) = y. In other words, it maps each element of the codomain (the output of the function) onto exactly one element of the domain (the input). For example, consider a function f from the set R of real numbers to itself defined by f(x) = 2x + 1 for