Add proof that RingAsCategory has a preadditive structure

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (397506a) 81.44% compared to head (b582085) 81.44%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1567 +/- ## ======================================= Coverage 81.44% 81.44% ======================================= Files 489 489 Lines 64302 64302 ======================================= Hits 52371 52371 Misses 11931 11931 ``` | [Flag](https://app.codecov.io/gh/homalg-project/CAP_project/pull/1567/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=homalg-project) | Coverage Δ | | |---|---|---| | [ActionsForCAP](https://app.codecov.io/gh/homalg-project/CAP_project/pull/1567/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=homalg-project) | `64.09% <ø> (ø)` | | | [AttributeCategoryForCAP](https://app.codecov.io/gh/homalg-project/CAP_project/pull/1567/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=homalg-project) | `88.88% <ø> (ø)` | | | [CAP](https://app.codecov.io/gh/homalg-project/CAP_project/pull/1567/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=homalg-project) | `84.63% <ø> (ø)` | | | [CartesianCategories](https://app.codecov.io/gh/homalg-project/CAP_project/pull/1567/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=homalg-project) | `93.33% <ø> (ø)` | | | [CompilerForCAP](https://app.codecov.io/gh/homalg-project/CAP_project/pull/1567/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=homalg-project) | `95.96% <100.00%> (ø)` | | | [ComplexesAndFilteredObjectsForCAP](https://app.codecov.io/gh/homalg-project/CAP_project/pull/1567/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=homalg-project) | `73.60% <ø> (ø)` | | | [FreydCategoriesForCAP](https://app.codecov.io/gh/homalg-project/CAP_project/pull/1567/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=homalg-project) | `81.17% <ø> (ø)` | | | [GeneralizedMorphismsForCAP](https://app.codecov.io/gh/homalg-project/CAP_project/pull/1567/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=homalg-project) | `61.60% <ø> (ø)` | | | [GradedModulePresentationsForCAP](https://app.codecov.io/gh/homalg-project/CAP_project/pull/1567/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=homalg-project) | `44.58% <ø> (ø)` | | | [GroupRepresentationsForCAP](https://app.codecov.io/gh/homalg-project/CAP_project/pull/1567/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=homalg-project) | `72.05% <ø> (ø)` | | | [HomologicalAlgebraForCAP](https://app.codecov.io/gh/homalg-project/CAP_project/pull/1567/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=homalg-project) | `73.21% <ø> (ø)` | | | [InternalExteriorAlgebraForCAP](https://app.codecov.io/gh/homalg-project/CAP_project/pull/1567/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=homalg-project) | `93.08% <ø> (ø)` | | | [LinearAlgebraForCAP](https://app.codecov.io/gh/homalg-project/CAP_project/pull/1567/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=homalg-project) | `66.72% <ø> (ø)` | | | [ModulePresentationsForCAP](https://app.codecov.io/gh/homalg-project/CAP_project/pull/1567/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=homalg-project) | `68.46% <ø> (ø)` | | | [ModulesOverLocalRingsForCAP](https://app.codecov.io/gh/homalg-project/CAP_project/pull/1567/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=homalg-project) | `90.70% <ø> (ø)` | | | [MonoidalCategories](https://app.codecov.io/gh/homalg-project/CAP_project/pull/1567/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=homalg-project) | `90.59% <ø> (ø)` | | | [ToricSheaves](https://app.codecov.io/gh/homalg-project/CAP_project/pull/1567/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=homalg-project) | `21.79% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=homalg-project#carryforward-flags-in-the-pull-request-comment) to find out more.

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