iex(1)> [1, 2, 3] ++ [4, 5, 6]
[1, 2, 3, 4, 5, 6]
iex(2)> Enum.concat([[1, [2], 3], [4], [5, 6]])
[1, [2], 3, 4, 5, 6]
iex(3)> Enum.concat([1..3, [4,5,6], 7..9])
[1, 2, 3, 4, 5, 6, 7, 8, 9]