anchor.diff:          /// </summary>
           | TooManyIteratedFuncs of view : DView * amount : int
           /// <summary>
  +        ///     An non-iterated func is being used in an iterated manner.
  +        /// </summary>
  +        | IteratorOnNonIterated of func : IteratedDFunc
  +        /// <summary>
           ///     A definition contains both iterated and non-iterated funcs.
           ///
           ///     <para>
  
positive.code: ///     </para>
  /// </summary>
  module Downclosure =
      /// <summary>
      ///     Performs all downclosure and well-formedness checking on iterated
      ///     constraints.
      /// </summary>
      let check (definer : ViewDefiner<BoolExpr<Sym<Var>> option>)
          : Result<ViewDefiner<BoolExpr<Sym<Var>> option>, Error> =
          // TODO (CaptainHayashi): implement
          ok definer
  
  /// Splits an iterated GFunc into a pair of guard and iterated func.
  let iterGFuncTuple
  
negative.code:         ///     </para>
          /// </summary>
          | MixedFuncType of view : DView
          /// <summary>
          ///     A view occurred in a constraint that does not exist.
          ///
          ///     <para>
          ///         Usually this will be caught earlier on, but this is here
          ///         to make sure.
          ///     </para>
          /// </summary>
          | NoSuchView of name : string
          /// <summary>
          ///     A view lookup failed during downclosure checking.
          ///
          ///     <para>
          ///         Usually this will be caught earlier on, but this is here
          ///         to make sure.
          ///     </para>
          /// </summary>
          | LookupError of name : string * err : Core.Instantiate.Types.Error
  
  
  /// <summary>
  