anchor.diff:                  let mapped = mapping.Invoke (x, y)
                   Set.add mapped mappedSet))
   
  -    //
  +    /// <summary>
  +    /// Applies the given function to each element in the Cartesian product of two sets. 
  +    /// Returns the set comprised of the results <c>x</c> for each element where the
  +    /// function returns <c>Some(x)</c>.
  +    /// </summary>
       [<CompiledName("Choose")>]
       let choose (chooser : 'T1 -> 'T2 -> 'U option) set1 set2 : Set<'U> =
           // Preconditions
  
positive.code:         Set.toSeq set
          |> Seq.tryFind predicate
  
  //
  [<CompiledName("Find")>]
  let find (predicate : 'T -> bool) (set : Set<'T>) : 'T =
      // Preconditions
  
negative.code:             |> Set.iter (fun y ->
                  action.Invoke (x, y)))
  
      /// Builds a new collection whose elements are the results of applying the given function
      /// to the elements in the Cartesian product of two sets.
      [<CompiledName("Map")>]
      let map (mapping : 'T1 -> 'T2 -> 'U) set1 set2 : Set<'U> =
          // Preconditions
  