public static bool IsDuplicate(ImmutableSortedDictionary <Position, SudokuElement> elements) => elements
.GroupBy(n => n.Value.Number)
.Where(n => n.Key != Data.Empty)
.Select(num => new { Value = num.Key, Total = num.Count() })
.Select(n => n.Total)
.Where(n => n > 1)
.Count() > 0;