Set Theory : $4$ Sets problem : Maxima and Minima in $4$ sets
4505
Number of students in school club : $4$ Circles Venn Diagram Puzzle
89712
For every set $A$, the empty set is a subset of $A$. The empty set is a set. Therefore, the empty set has a cardinality $\geq 1\ldots$
79568
Cardinality of the set $D$
153072
Guessing a subset of $\{1,...,N\}$
28391
Prove the compactness of a set B
32441
How to prove or disprove statements about sets
121366
Intervals and cardinality
88595
Prob. 21, Sec. 17 in Munkres' TOPOLOGY, 2nd ed: Closure and complementation can result in at most 14 different sets
57785
Finding all maxima and minima of a function
100565
Property of sup of a set of numbers
12701
Perfect set without rationals
25834
Proof a set cannot contain its own powerset - Russell's Paradox
7112
Product of sets and supremum
126015
Elementary number theory in sets
79974
The cardinality of Lebesgue sets
114262
Find the cardinality of the following set $S_n=\{(x,y)|x^2+y^2=n, \text{where }x,y,n \in \mathbb Z\text{ and }n\geq0 \}$
107964
Simple combinatorics problem.