anchor.diff:      /// predicate holds. The predicate is evaluated asynchronously.
       [<CompiledName("TakeWhileAsync")>]
       let rec takeWhileAsync predicate (input : AsyncSeq<'T>) : AsyncSeq<'T> =
  +        // Preconditions
  +        checkNonNull "input" input
  +
           async {
           let! v = input
           match v with
  
positive.code:     /// The specified function is asynchronous (and the input sequence will
      /// be asked for the next element after the processing of an element completes).
      [<CompiledName("MapAsync")>]
      let mapAsync mapping (input : AsyncSeq<'T>) : AsyncSeq<'TResult> =
          asyncSeq {
          for itm in input do
              let! v = mapping itm
  
negative.code:     /// be asked for the next element after the processing of an element completes).
      [<CompiledName("ChooseAsync")>]
      let chooseAsync chooser (input : AsyncSeq<'T>) : AsyncSeq<'U> =
          // Preconditions
          checkNonNull "input" input
  
          asyncSeq {
          for itm in input do
              let! v = chooser itm
  