Algebraic quotients #

This file defines notation for algebraic quotients, e.g. quotient groups G ⧸ H, quotient modules M ⧸ N and ideal quotients R ⧸ I.

The actual quotient structures are defined in the following files:

Quotient Group: Mathlib/GroupTheory/Cosets/Defs.lean
Quotient Module: Mathlib/LinearAlgebra/Quotient/Defs.lean
Quotient Ring: Mathlib/RingTheory/Ideal/Quotient/Defs.lean

Notation #

The following notation is introduced:

G ⧸ H stands for the quotient of the type G by some term H (for example, H can be a normal subgroup of G). To implement this notation for other quotients, you should provide a HasQuotient instance. Note that since G can usually be inferred from H, _ ⧸ H can also be used, but this is less readable.

Tags #

quotient, group quotient, quotient group, module quotient, quotient module, ring quotient, ideal quotient, quotient ring

source

class HasQuotient (A : outParam (Type u)) (B : Type v) :

Type (max (u + 1) (v + 1))

HasQuotient A B is a notation typeclass that allows us to write A ⧸ b for b : B. This allows the usual notation for quotients of algebraic structures, such as groups, modules and rings.

A is a parameter, despite being unused in the definition below, so it appears in the notation.

Quotient : B → Type (max u v)
HasQuotient.Quotient A b (denoted as A ⧸ b) is the quotient of the type A by b.
This differs from HasQuotient.quotient' in that the A argument is explicit, which is necessary to make Lean show the notation in the goal state.