Concept · Foundations
Subset
A set A is a subset of a set B, written A ⊆ B, if every element of A is also an element of B; A is a proper subset if in addition A ≠ B.
Why it matters
The subset relation is how set theory expresses class inclusion, and distinguishing it from membership is essential to avoid foundational confusion.
Where this shows up
Units and lessons using this concept
Following the links will take you to the page where this term is introduced in context.
Related