Final answer:
The function f(m, n) = m + n is onto since for every integer y in the codomain, there exist integers m and n whose sum is y, showing that every integer can be the result of the function.
Step-by-step explanation:
When determining whether the function f: ×→ ℕ is onto for the case of f(m, n) = m + n, we must consider whether every possible value in the codomain (which in this case is the set of all integers, ℕ) can be obtained by applying the function to some element in the domain. The function in question takes two integers m and n and returns their sum.
To see if the function is onto, we must verify if for every integer y in the codomain, there exist integers m and n such that m + n = y. Given any integer y, we can always find two integers m and n such that their sum is y (e.g., m = y and n = 0, or m = 0 and n = y). Therefore, the function is indeed onto.