Can a surjective function $f: \mathbb N\to \mathbb N $ be not injective?
117793
Finding a function $\mathbb{N} \to \mathbb{N}$ that is surjective but not injective.
72115
Why isn't there a continuously differentiable surjection from $I \to I \times I$?
134104
Is there a Cantor-Schroder-Bernstein statement about surjective maps?
70912
If $g\circ f$ is injective and $f$ is surjective then $g$ is injective
93040
$f$ is surjective iff it has a right inverse: using the axiom of choice and errors in ProofWiki
146306
A continuous surjective function from $(0,1]$ onto $[0,1]$
122160
$f:\mathbb R \to \mathbb R$ be a continuous such that $f(f(f(x)))=x,\forall x \in \mathbb R$ , is $f(x)=x , \forall x \in \mathbb R$?
117502
Proving that a certain continuous function is surjective.
111689
Surjective, but not injective endomorphism
63146
Proof of properties of injective and surjective functions.
45792
Rigorous proof that surjectivity implies injectivity for finite sets
6825
If $f: \mathbb Q\to \mathbb Q$ is a homomorphism, prove that $f(x)=0$ for all $x\in\mathbb Q$ or $f(x)=x$ for all $x$ in $\mathbb Q$.
20199
Find a surjective function $f:\mathbb{N}\to \mathbb{Q}$
79285
Does there exist a continuous surjection from $\Bbb R^3-S^2$ to $\Bbb R^2-\{(0,0)\}$?
124333
A bijection between $\mathbb{N}$ and $\mathbb{P}(\mathbb{N})$?
20303
A function $f\colon E\to F$ between finite sets is injective iff it is surjective iff it is bijective
7036
Is there a bijective continuous function $f: \Bbb R \to \Bbb R$ whose inverse $f^{-1}$ is not continuous?