anchor.diff:  
     /// Helper function used when building frames from data tables
     let createTypedVector : _ -> seq<OptionalValue<obj>> -> _ =
  -    let cache = Dictionary<_, _>()
  +    let cache = ConcurrentDictionary<_, _>()
       (fun typ ->
         match cache.TryGetValue(typ) with
         | true, res -> res
  
positive.code:           let par = Expression.Parameter(typeof<seq<OptionalValue<obj>>>)
            let body = Expression.Call(createTypedVectorMi.MakeGenericMethod([| typ |]), par)
            let f = Expression.Lambda<Func<seq<OptionalValue<obj>>, IVector>>(body, par).Compile()
            cache.Add(typ, f.Invoke)
            f.Invoke )
  
    let getExpandableProperties (ty:Type) =
  
negative.code:   open Microsoft.FSharp.Quotations
    open System.Collections
    open System.Collections.Generic
    open System.Collections.Concurrent
  
    let indexBuilder = IndexBuilder.Instance
    let vectorBuilder = VectorBuilder.Instance
  