Is $∅$ proper subset of $\{\{∅\}\}$?
31376
If null set is an element of a set then will it belongs to set or subset?
70143
Mutually exclusive countable subsets of a countable set
126015
Elementary number theory in sets
153551
Is the null set a subset of every set?
59813
Prove that for all sets A and B, A ∩ B = ∅ implies ( A ∪ B ) - B = A
109374
Is the Discrete Topology on $X$ the Only One Containing All Infinite Subsets of $X$?
132025
Is there an alternative to Cantor's cardinalities that makes proper subsets smaller than their sets?
136755
Direct proof of empty set being subset of every set
124060
Are these subsets of the powerset P(N) countable?
19856
Prove that a subset of a separable set is itself separable
74860
Why is the empty set a subset of every set?
131983
Prove that $A \subset B$ if and only if $A \setminus B = \emptyset$
117561
A set is infinite iff there is a one-to-one correspondent with one of its proper subsets?
48162
Is the subset $[0, \sqrt2] ∩\mathbb{Q} ⊂ \mathbb{Q}$ closed, bounded, compact?
80827
Let $A$ be a nonempty subset of $\mathbb{R}$. Prove...
140668
Union of $2$ set $A, B$ where $ A$ is a subset of $B$
67279
Is the union of finitely many open sets in an omega-cover contained within some member of the cover?