Categories and functors with a concrete group example
Research context
postgraduate concept · established · As of 2026-10-10
A category has objects, composable morphisms, associative composition and an identity for every object.
Key knowledge
A category has objects, composable morphisms, associative composition and an identity for every object. A functor preserves identities and composition. A group is a one-object category with all arrows invertible; a representation G→GL(V) is a functor to a vector-space category restricted to that object. Objects and hom-collections have declared size conventions to avoid treating every collection as a set.
Conditions and scope
- A locally small category has a set of arrows between each pair of objects; the collection of objects may be larger.
- Composition order is fixed; functors preserve the structural maps exactly here.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Author checked this English statement, displayed equation where present and stated hypotheses against these source locations: §§1.1–1.4 categories/functors/naturality, §2.2 Yoneda, chapter 4 adjunctions. The check is bounded to the recorded claims; no complete proof reconstruction, software proof replay or universal literature completeness is claimed.
2026-10-10 · Author source-body/statement/equation/domain check, with graph associations scoped individually. Separate independent content/source/inventory review is required before branch closure.
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