396             foreach (var element in source)  in IndexOf()
398                 if (predicate(element))  in IndexOf()
410             foreach (var element in revSource)  in LastIndexOf()
412                 if (predicate(element))  in LastIndexOf()
518             foreach (var element in source)  in DistinctBy()
520                 if (knownKeys.Add(keySelector(element)))  in DistinctBy()
522                     yield return element;  in DistinctBy()
531         public static IEnumerable<T> Append<T>(this IEnumerable<T> source, params T[] element)  in Append()  argument
537             return ConcatIterator(element, source, false);  in Append()
1626         public static bool TryGetNext<T>(this IEnumerator<T> @this, out T element)  in TryGetNext()  argument
1628             element = default(T);  in TryGetNext()
1631                 element = @this.Current;  in TryGetNext()