Calculate the number $o(\mathbb{R})$ of open subsets of the real line.
92639
Prove that the family of open sets in $\mathbb{R}$ has cardinality equal to $2^{\aleph_0}$
146098
Number of nonempty subsets of a set with $n$ elements
44704
familly of Radially open sets in $\mathbb{R}^2$
102510
Count number of subsets of 3 elements either disjoint or whose intersection is a singleton
21599
$(0,1)$ is an open subset of $\mathbb{R}$ but not of $\mathbb{R}^2$, when we think of $\mathbb{R}$ as the x-axis in $\mathbb{R}^2$. Prove this.
114370
I want to figure out how many Topologies are in the set X
44214
The number of subsets of a set of cardinality $n$
26569
Counting binary operations on a set with $n$ elements
100437
Classification of connected subsets of the real line (up to homeomorphism)
85681
Cardinality of polynomials with real coefficients
22232
Proving that cardinality of the reals = cardinality of $[0,1]$
1396
cardinality of all real sequences
27855
Show that $(a,b)\times (c,d)$ is an open set in $\mathbb{R}^2$ with the Euclidian metric.
12003
Cardinality of set of real continuous functions
102972
Cardinality of $\mathbb{R}^\mathbb{R}$ by diagonal argument
86914
Cardinality of the set of hyperreal numbers
73130
A simple question about open set