| ExceptByTSource, TKey(IEnumerableTSource, IEnumerableTSource, FuncTSource, TKey) | Returns the set of elements in the first sequence which aren't in the second sequence, according to a given key selector. |
| ExceptByTSource, TKey(IEnumerableTSource, IEnumerableTSource, FuncTSource, TKey, IEqualityComparerTKey) | Returns the set of elements in the first sequence which aren't in the second sequence, according to a given key selector. |