Why $\{\emptyset\} \not \subset\{\{\emptyset\}\}$?
858
Is $\{\emptyset\}$ a subset of $\{\{\emptyset\}\}$?
36721
Is "The empty set is a subset of any set" a convention?
68244
Is ∅ equivalent to {∅}?
58594
Is the empty set a subset of itself?
118824
What is the complement of empty set?
136755
Direct proof of empty set being subset of every set
58285
Is it true that if $X$ is connected, then for every nonempty proper subset $A$ of $X$, we have $\mathbf{Bd} \ne \emptyset$
56637
In naive set theory ∅ = {∅} = {{∅}}?
14512
Why cannot a set be its own element?
9850
How many ways are there to choose 3 subsets $A,B,C$ of a set $\{1,2,3...n\}$ such that $ A \cap B \cap C = \emptyset $
141318
$\subset$ vs $\subseteq$ when *not* referring to strict inclusion
134050
Question about set notation: what does $]a,b[$ mean?
34099
Proving that the empty set is unique
131983
Prove that $A \subset B$ if and only if $A \setminus B = \emptyset$
130418
Is ${\{\emptyset,\{\emptyset\},\{\{\emptyset\}\},\{\{\{\emptyset\}\}\},...\}} $ a set?
78300
Showing a set is closed other than giving a counterexample?
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 $\geq 1\ldots$