Matt Fishman

@ogauthe I realized that one reason to keep `UnitRangeDual` is that it may be a reasonable return type when slicing blocks of a `GradedUnitRangeDual`, i.e. it might make sense for...

I agree with your assessment that `UnitRangeDual` should be a subtype of `AbstractUnitRange`, and also that we should be thoughtful about which operations create `UnitRangeDual`. I'll try to summarize that...

This is copied from this comment: https://github.com/ITensor/ITensors.jl/pull/1363#discussion_r1774410848: It would be nice to think through how functions like: ```julia flip(g::AbstractGradedUnitRange) = dual(gradedrange(label_dual.(blocklengths(g)))) ``` could be written in a simpler way. One...

@ogauthe probably at this point it makes more sense to define: ```julia abstract type AbstractGradedUnitRange{T,CS}

> Indeed we would have more freedom with `abstract type AbstractGradedUnitRange{T,CS} `. Just to be clear, that would be a significant change in the implementation. It seems to me that...

> Concerning `dual`, if I remember correctly, the rational behind `UnitRangeDual` was precisely to have `GradedUnitRange = BlockedUnitRange{LabelledInteger}`, at a time when `BlockArrays` did not define `AbstractBlockedUnitRange`. Now we have...

I don't have a good guess without digging into the code... I had to track down a lot of issues like that before, usually it is just a missing overload.

> Indeed the problems come from missing overload for `BlockArrays.combine_blockaxes`. Fixing it in a generic way should solve many related issues in ITensor/BlockSparseArrays.jl#2 . Great! Glad to hear you tracked...

> The other problems where due to the change `blockedunitrange_getindices/gradedunitrange_getindices`. Maybe I should avoid defining `gradedunitrange_getindices` and just specialize `blockedunitrange_getindices` for `AbstractGradedUnitRange`. That seems simpler, for context the primary purpose...

@ogauthe this PR looks good to me, given the current type hierarchy that we are aiming for right now. I definitely get your point about there being a lot of...