when is a function said to be onto
Surjective function In mathematics, a function f from a set X to a set Y is surjective (or onto), or a surjection, if for every element y in the codomain Y of f there is at least one element x in the domain X of f such that f(x) = y. It is not required that x is unique; the function f may map one or more elements of X to the same element of Y.
On Top of the World (Imagine Dragons song) "On Top of the World" is a song by the American rock band Imagine Dragons for their major-label debut extended play Continued Silence (2012), where it appears as the third track. The song also appears on their debut studio album Night Visions (2012) as the fifth track. "On Top of the World" was released digitally as a single on March 18, 2013.