anchor.diff:  
           //
           [<CompiledName("Choose")>]
  -        let choose (separator : char[], options : System.StringSplitOptions)
  -                (chooser : substring -> string option) (str : string) : string[] =
  +        let choose (separator : char[]) (chooser : substring -> 'T option) (str : string) : seq<'T> =
               // Preconditions
               checkNonNull "str" str
   
  
positive.code: 
  open System
  //open System.Diagnostics.Contracts
  
  
  /// Represents a segment of a string.
  
negative.code:     /// Returns the characters in the given substring as a Unicode character array. 
      [<CompiledName("ToArray")>]
      let inline toArray (substr : substring) : char[] =
          substr.ToCharArray ()
  
      /// Determines whether the beginning of a substring matches the specified string.
      [<CompiledName("StartsWith")>]
      let inline startsWith (value : string) (substr : substring) : bool =
          substr.StartsWith value
  
      /// Determines whether the end of a substring matches the specified string.
      [<CompiledName("EndsWith")>]
      let inline endsWith (value : string) (substr : substring) : bool =
          substr.EndsWith value
  
      /// Extracts the first (left-most) character from a substring, returning a Some value
      /// containing the character and the remaining substring. Returns None if the given
  