anchor.diff:  
     let index = Lazy.Create(fun () ->
       let count = int (max - min).TotalDays 
  -    let keys = [| for i in 0 .. count - 1 -> min.AddDays(float i) |]
  +    let keys = [| for i in 0 .. count -> min.AddDays(float i) |]
       Linear.LinearIndexBuilder.Instance.Create(keys, Some true) )
   
     interface IIndex<DateTime> with
       member x.Keys = index.Value.Keys
  -    member x.Lookup(key, semantics) = index.Value.Lookup(key, semantics)
  +    member x.Lookup(key, semantics) = printfn "Lookup %A" key; index.Value.Lookup(key, semantics)
       member x.Mappings = index.Value.Mappings
       member x.Range = index.Value.Range
       member x.Ordered = index.Value.Ordered
       member x.Comparer = index.Value.Comparer
  +
  +  member x.Minimal = min
  +  member x.Maximal = max
   
   type LazyIndexBuilder() =
     let builder = Linear.LinearIndexBuilder.Instance
  
positive.code: let s2 = s1.[DateTime(2013,1,1) .. ]
  let s3 = s2.[ .. DateTime(2013,2,1)]
  
  s3.Count
negative.code:   let vector = Lazy.Create(fun () ->
      printfn "QUERY: %A to %A" min max
      let count = int (max - min).TotalDays 
      let data = [| for i in 0 .. count -> 3.0 |]
      ArrayVector.ArrayVectorBuilder.Instance.CreateNonOptional(data) )
  
    member x.Minimal = min
  