anchor.diff:          (shouldNotMsg : string) =
       { new Matcher<'T> () with
           member __.ApplyActual g actual = f actual |> g
  -        member __.FailureMsgForShould = shouldMsg
  -        member __.FailureMsgForShouldNot = shouldNotMsg
  +        member __.ExpectationMsgForShould = shouldMsg
  +        member __.ExpectationMsgForShouldNot = shouldNotMsg
       }
   
   let createMatcher<'T> (f : 'T -> MatchResult) (shouldMsg : string) =
  
positive.code:         match a.ApplyActual id actual with
          | MatchSuccess x -> b.ApplyActual id (x :?> 'b)
          | x -> x
      createMatcher f (sprintf "%s %s" a.FailureMsgForShould b.FailureMsgForShould)
negative.code: module have =
      let atLeastOneElement matcher =
          let f a = a |> Seq.exists (Matcher.IsMatch matcher)
          let msg = sprintf "contain at least one element to %s" matcher.ExpectationMsgForShould
          let notMsg = sprintf "contain no elements to %s" matcher.ExpectationMsgForShould
          createFullBoolMatcher f msg notMsg
  
      let element = atLeastOneElement
  