1. The problem statement, all variables and given/known data It is in some notes that I found online in an attempt to understand something else that I need to know for a math course. 2. Relevant equations f : ℕ → ℕ 3. The attempt at a solution It seems to mean that a function of some natural number will equal some other natural number such as n^2 where n is an element of the naturals. But I am not sure.