The Azimuth Project
2-Rig (Rev #3, changes)

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A ring is a set equipped with two binary operations, addition and multiplication, where the addition makes the set a group, and the multiplication distributes over addition. A rig is nearly the same, but we don’t demand additive inverses. A 2-rig is a categorification of rigs, where we give a category a notion of addition and multiplication which obeys a distributive law. The thing which corresponds to addition is the existence of all small colimits, and the thing which corresponds to multiplication is a symmetric monoidal structure.


I think the word “2-rig” was first used in HDAIII.

A 2-rig is a symmetric monoidal cocomplet category for which the monoidal structure preserves small colimits in each argument.


  • Set\mathsf{Set}, the category of sets and functions is a 2-rig with its cartesian monoidal structure.

  • Vect\mathsf{Vect}, the category of vector spaces (over some chosen field) and linear maps is a 2-rig with tensor product giving the monoidal structure.