Hi, Simple excerise: You have a sorted list of integers: l=[1, 2, 4, 7, 8, 12] and you should fill all gaps: result == [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12] How would you code this? Constrain: The original list should be changed, don't create a copy. thomas