📝 **Task:** Write `three_sum(nums)` returning all unique triplets summing to 0. Print `three_sum([-1, 0, 1, 2, -1, -4])`. Expected: [[-1, -1, 2], [-1, 0, 1]] 📋 Implement the function above. Tests run automatically. 💡 **Hint:** Re-read the theory if stuck.