anchor.diff:  
       /// Perform a sort on elements, preserving order of equal elements.
       let sortStable (arr : _ array) =
  -        arr |> Seq.sort |> Array.ofSeq+        arr |> Seq.sort |> Array.ofSeq
  
positive.code:         Array.Copy (arr, 0, arr2, 1, tailLength)
          arr2
  
      /// Add (or 'snoc) a value to the end of an array.
      let add elem arr =
          let tailLength = Array.length arr
          let arr2 = Array.zeroCreate (inc tailLength)
  
negative.code: [<RequireQualifiedAccess>]
  module Array =
  
      /// Add a value to the front of an array.
      let cons elem arr =
          let tailLength = Array.length arr
          let arr2 = Array.zeroCreate (inc tailLength)
  