Past exam of the year 1 of the computer science course of the University of Oxford / 2015 / Discrete mathematics, continuous mathematics, and probability (resit) / 1 / a

The image of a function $f:A\to B$ isThe function is surjective, or onto, exactly when every $b\in B$ equals $f(a)$ for at least one $a\in A$, equivalently $f(A)=B$. It is injective, or one-to-one, exactly whenThus surjectivity concerns whether the entire codomain is reached; injectivity concerns whether distinct inputs have distinct outputs.