| Flatten(IEnumerable) | Flattens a sequence containing arbitrarily-nested sequences. |
| Flatten(IEnumerable, Func<IEnumerable, Boolean>) | Flattens a sequence containing arbitrarily-nested sequences. An additional parameter specifies a predicate function used to determine whether a nested IEnumerable should be flattened or not. |
| Flatten(IEnumerable, Func<Object, IEnumerable>) | Flattens a sequence containing arbitrarily-nested sequences. An additional parameter specifies a function that projects an inner sequence via a property of an object. |