Part 1: You must write a function called list-leveller. List-leveller function takes a (nested) list as an input and converts the input (nested) list to a list which does not contain any list(s).
Part 2: You must write a function called merge-list. Merge-list function takes two lists as inputs and merges the lists. Output must be a list.
Part 2 Restriction: You are not allowed to use append function for this part.
Part 3: Write a function called insert-n which takes a list, a number and an index as inputs, then inserts the number to the specified index in the list. Note that the i-th value in original list should not be overwritten.
