Export the `isinvertible` and `inverse` functions

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Codecov Report

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

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #287 +/- ## ========================================= Coverage ? 94.95% ========================================= Files ? 48 Lines ? 1388 Branches ? 0 ========================================= Hits ? 1318 Misses ? 70 Partials ? 0 ```

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