The thing is, for
Set, you need not just equality but comparison. And you can't really do comparison by reference in .NET. So I think you have 2 choices. 1: Add a Guid to BigType, fill it with Guid.NewGuid() when you create a value, and implement a custom comparison on BigType that compares this Guid. The structural comparison on CollectionType will use this custom comparison. 2: switch from Set to Dictionary, which only needs equality and can be referential, but of course works with mutation so it may not be appropriate in your case.
