Union of $2$ set $A, B$ where $ A$ is a subset of $B$
47434
Proof that $A \subseteq B \Leftrightarrow A \cup B = B$
50880
Expressing $\Bbb N$ as an infinite union of disjoint infinite subsets.
70940
Homework - set theory infinite union
13132
If the union of two sets is contained in the intersection, then one is contained in the other ($[A\cup B\subseteq A\cap B]\implies A \subseteq B$)
119084
How many ordered pairs $(A,B)$ they are if $A$ and $B$ are subsets of $\{ 1,2,3,4,5 \}$ such that $A \cap B = \{1\}$?
55023
if $A$ subset of $B$ then $P(B)-P(A)=P(B\setminus A)\ge 0$
75966
Prove that if $A$ is a set with $m$ elements, $B$ is a set with $n$ elements, and $A \cap B = \emptyset$, then $A \cup B$ has $m+n$ elements.
74077
A intersection (A union B)
134071
If A is a finite set and B is an infinite set, then B\A is an infinite set
79697
If $A$ is a subset of $B$, then the closure of $A$ is contained in the closure of $B$.
12404
Union of definable sets
11849
Size of a union of two sets
23225
Union of connected subsets is connected if intersection is nonempty
77902
If $A,B,$ and $C$ are sets, then $A\times(B-C)$ = $(A \times B)$ $-$ $(A \times C)$.
158498
$A\subset \mathbb{R}$ with more than one element and $A/ \{a\}$ is compact for a fixed $a\in A$
123613
Double Complement of a set proof
97697
Countable union of sets of cardinality $c$ has cardinality $c$