Show that there exist two separate sets..
104527
Prove that there are two subsets of any cardinality-10 subsets of $\{1,2\dots,106\}$ that sum to the same number
34099
Proving that the empty set is unique
11849
Size of a union of two sets
123090
How to show that disjoint closed sets have disjoint open supersets?
77286
Proving set theory question
30660
Empty set does not belong to empty set
57822
Number of ways to choose two disjoint subsets of a set
158671
Cardinality of a set that consists of all existing cardinalities
19289
complement of a set and its measure
7112
Product of sets and supremum
123897
Sum of two open sets is open?
142631
Show that A has the same cardinality as $A\setminus\{x,y,z\}$
83518
Proving Two sets have same cardinality
130156
Image of the union and intersection of sets.
148234
Express set $[a,b] \cup [c,d]$ as the difference of two intervals
24050
Characterization of the Closure of a Set
83996
For any two sets $A,B$ , $|A|\leq|B|$ or $|B|\leq|A|$