Definition
A⊂B
(and we say "A is a subset of B") if and only if every element of A
also belongs to B
That is: [A⊂B]⟺[x∈A⟹x∈B]
[1]
References
- Jump up ↑ Definition 3.10 (p10) - Introduction to Set Theory, Third Edition (Revised and Expanded) - Karel Hrbacek and Thomas Jech