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[Merged by Bors] - doc(init/algebra/classes): add a brief docstring #568

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[Merged by Bors] - doc(init/algebra/classes): add a brief docstring #568

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doc(init/algebra/classes): add a brief docstring
eric-wieser Apr 26, 2021
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12 changes: 12 additions & 0 deletions library/init/algebra/classes.lean
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Expand Up @@ -7,6 +7,18 @@ prelude
import init.logic init.data.ordering.basic
universes u v

/-!
# Unbundled algebra classes

These classes and the `@[algebra]` attribute are part of an incomplete refactor described
[here on the github Wiki](https://github.com/leanprover/lean/wiki/Refactoring-structures#encoding-the-algebraic-hierarchy-1).

By themselves, these classes are not good replacements for the `monoid` / `group` etc structures
provided by mathlib, as they are not discoverable by `simp` unlike the current lemmas due to there
being little to index on. The Wiki page linked above describes an algebraic normalizer, but it is not
implemented.
-/

@[algebra] class is_symm_op (α : Type u) (β : out_param (Type v)) (op : α → α → β) : Prop :=
(symm_op : ∀ a b, op a b = op b a)

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