https://learn.microsoft.com/en-us/dotnet/api/system.collections.immutable.immutablehashset.toimmutablehashset?view=dotnet-uwp-10.0&viewFallbackFrom=net-8.0
ImmutableHashSet.ToImmutableHashSet Method (System.Collections.Immutable) | Microsoft Learn
Enumerates a sequence and produces an immutable hash set of its contents.
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