You are given the starting 'l' and the ending 'r' positions of the array 'ARR'.You must sort the elements between 'l' and 'r'.

Here are the steps to sort the elements between 'l' and 'r' in an array 'ARR':

1. First, check if 'l' and 'r' are valid indices for the array 'ARR'. This means 'l' should be greater than or equal to 0 and less than the length of the array. Similarly, 'r' should be greater than 'l' and less than or equal to the length of the array.

2. Extract the subarray from 'ARR' that starts at index 'l' and ends at index 'r'. You can do this by using the slice operation: subarray = ARR[l:r+1].

3. Sort the subarray. Most programming languages have built-in functions to sort arrays. For example, in Python, you can use subarray.sort().

4. Replace the elements in the original array 'ARR' between indices 'l' and 'r' with the sorted subarray. You can do this by using a loop that iterates over the subarray and the original array simultaneously.

5. The array 'ARR' is now sorted between indices 'l' and 'r'.