Array collections offer various ways to access their elements.

The positions are 0 indexed. Objects of the array can be accessed using the [] method which may take various arguments, as explained below.

arr = [9, 5, 1, 2, 3, 4, 0, -1]

• A number which is the position of element

>>arr[4]
  => 3

or

>>arr.at(4)
  => 3 

• A range indicating the start and the end position

>>arr[1..3] # .. indicates both indices are inclusive. 
  => [5,1,2]
>>arr[1...3] # ... indicates the last index is excluded.
  => [5,1]

• Start index and the length of the range

>>arr[1,4]
  => [5, 1, 2, 3]

For this challenge, your task is to complete the functions using syntax as explained above.