essentially surjective
A functor is essentially surjective (on objects) when every object is isomorphic to for some object .
Dual essentially surjective (self-dual) Related dominant, equivalence, essentially injective External nLab link
Relevant implications
- implies essentially surjective
Examples
There are 19 functors with this property.
- abelianization functor for groups
- binary coproduct functor on sets
- binary product functor on sets
- enveloping group functor
- forgetful functor for topological spaces
- forgetful functor from groups to pointed sets
- fundamental group functor
- group of units functor
- identity functor on the category of sets
- morphism endpoints inclusion
- opposite category functor
- opposite monoid functor
- path components functor
- Stone-Čech compactification functor
- trivial functor from the category of groups
- trivial functor from the category of sets
- trivial functor from the delooping
- trivial functor from the walking idempotent
- walking isomorphism object inclusion
Counterexamples
There are 37 functors without this property.
- binary diagonal functor on the category of sets
- Brauer group functor
- contravariant power set functor
- countable copower functor on sets
- covariant power set functor
- discrete topology functor
- doubling functor on sets
- empty functor to the category of sets
- forgetful functor for groups
- forgetful functor for rings
- forgetful functor for vector spaces
- forgetful functor from abelian groups to groups
- forgetful functor from commutative rings to rings
- forgetful functor from finite abelian groups to abelian groups
- forgetful functor from finite groups to groups
- forgetful functor from finite sets to sets
- forgetful functor from groups to monoids
- forgetful functor from Hausdorff spaces to topological spaces
- forgetful functor from rings to monoids
- forgetful functor from torsion abelian groups to abelian groups
- forgetful functor from torsion-free abelian groups to abelian groups
- free group functor
- functor of continuous functions
- inclusion functor from extended natural numbers to ordinal numbers
- indiscrete topology functor
- modulo p functor
- monoid ring functor
- nerve functor
- p-torsion functor
- rational product functor
- ring idempotents functor
- sequences functor on sets
- simple-group probing functor
- span endpoints inclusion
- squaring functor on sets
- torsion functor
- walking morphism representation
Unknown
There are 0 functors for which the database has no information on whether they satisfy this property.
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