...  ...  @@ 36,9 +36,17 @@ IWR Heidelberg 


* `namespace Dune::Functions::BasisBuilder` should become `namespace Dune:Functions::Bases`.



* `LocalIndexSet::bind()` should fill an internal cache with the indices. `LocalIndexSet::index()` should be cheap and only look up the index in the internal cache. This can be implemented now in `DefaultLocalIndexSet`.



* `NodeIndexSet` should be extended by a method for batch filling all indices into an external buffer.



* To implement nonaffine FE spaces and transformations (like, e.g. for RaviartThomas)



we want to add the following functionality. The exact interface has to be discussed.



As a first step we will launch the RT implementation and try to add these



one by one.



* Add an interface to obtain a pointwise local transformation for the range space for each node. (e.g. the Piolatransformation for RT)



* Add an interface to obtain a linear basis transformation for each node. This allows, e.g., to flip basis functions (normal flip for RT), to permute basis functions or, in general, to transform to another local basis.



* Add an interface to obtain a "global" finite element which already contains the range space transformation and the element geometry transformation of the domain. It should not contain the basis transformation, because this can be done more efficiently outside.






### TypeTree



* Add a method `treePath(...)` that does the same as `hybridTreePath()`



* Get rid of `TreePath` and `DynamicTreePath`



* Derive from/wrap `TupleVector` in `HybridTreePath`



* Get rid of `backIndex()` if possible 


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* Get rid of `backIndex()` if possible



