New posts in Elementary Set Theory

Prove or Disprove : There exists a continuous bijection from $\mathbb{ R}^2$ to $\mathbb{R} $

Can anyone please help me to understand what does "well-defined" mean in the definition of Set?

Countability of a sequence of natural numbers

Equivalence between two definitions of closure of $A\subseteq B$ under a function $f\colon B\to B$

Difference between a number and a set with one number

Definition of a bounded, nonempty subset of real numbers.

If $T_n = \{\frac{a}{n} \mid a \in \mathbb{Z}\}$, then what are $\bigcup_{n\in\mathbb{N}}T_n$ and $\bigcap_{n\in\mathbb{N}}T_n$?

Is "False" in logic analogous to "Null set" in set theory?

What is a relation in plain simple English?

Prove that $A \cup C \subseteq B \cup C$ iff $A \setminus C \subseteq B \setminus C$