## `Cat::CommutativeRing` -- the category of commutative rings

#### Introduction

`Cat::CommutativeRing` represents the category of commutative rings.

#### Generating the category

`Cat::CommutativeRing()`

#### Categories

`Cat::Ring`

, `Cat::RightModule(dom)`

#### Details

- A `Cat::CommutativeRing` is a ring with unit `dom::one` where the multiplication `*` (`_mult`) is commutative. It is also a right module over itself.
- This implementation additionally assumes that the elements are always constant with respect to differentiation and derivates. One must re-implement the methods `"diff"` and `"D"` if this assumption is false.

#### Method diff: differentiates element

- `diff(dom x <, variable v...>)`
- - This implementation always returns 0.

#### Method D: returns derivative

- `D(Type::ListOf(Type::PosInt) l, dom x)`
- - This implementation always returns 0.

#### Changes

- New methods: `"diff"` and `"D"`.

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