Newbetuts
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New posts in elementary-set-theory
Does a map between topologies determine a map between sets?
general-topology
elementary-set-theory
Composition of injections (proof)
functions
elementary-set-theory
Number of functions $f : A \to A$ such that $f(f(x))=f(x)$
combinatorics
functions
elementary-set-theory
Codomain as part of the definition of a function
functions
elementary-set-theory
soft-question
definition
Is $\mathbb{Z}= \{\dots -3, -2, -1, 0 ,1 ,2 , 3, \dots \}$ countable?
real-analysis
elementary-set-theory
Why is $\mathcal{P}(A\cup B) \not\subset \mathcal{P}(A)\cup\mathcal{P}(B)$?
elementary-set-theory
solution-verification
fake-proofs
If $f : A \to B$ and $B$ is countable, given that $f$ is surjective, $A$ is countable.
real-analysis
elementary-set-theory
Proof that sets are equal
proof-verification
elementary-set-theory
Cardinality and infinite sets: naturals, integers, rationals, bijections
elementary-set-theory
cardinals
Bijections from $A$ to $B$, where $A$ is the set of subsets of $[n]$ that have even size and $B$ is the set of subsets of $[n]$ that have odd size [duplicate]
combinatorics
elementary-set-theory
(Finitely) decimal expressible real numbers between [0,1] countable?
elementary-set-theory
discrete-mathematics
Prove that $\mathcal{P}(A)\cup \mathcal{P}(B) \subseteq \mathcal{P}(A\cup B)$.
elementary-set-theory
proof-writing
Can we find a well ordering on an infinite set with no largest element?
elementary-set-theory
well-orders
Uniqueness proof for $\forall A\in\mathcal{P}(U)\ \exists!B\in\mathcal{P}(U)\ \forall C\in\mathcal{P}(U)\ (C\setminus A=C\cap B)$
elementary-set-theory
proof-writing
$R$ is transitive if and only if $ R \circ R \subseteq R$
elementary-set-theory
relations
equivalence-relations
function-and-relation-composition
Suppose $A \subseteq P(A)$. Prove that $P(A)\subseteq P(P(A))$
elementary-set-theory
solution-verification
When is $ A \subseteq \mathcal{P} (A)$?
elementary-set-theory
How do i write "The set of sequence B contains all possible order of item in the set A"? [closed]
sequences-and-series
elementary-set-theory
notation
What is the interior of a singleton?
general-topology
elementary-set-theory
An easy to understand definition of $\omega_1$?
general-topology
elementary-set-theory
cardinals
ordinals
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