#Create a list
lst = [1,3,5,6,7,7]
#index element at 4-2 (which is 2)
lst[4-2] # returns 5
#index element at 2-4 (which is -2) or lst[len(lst)-2]
lst[4-2] # returns 7

lst <- c(1,3,5,6,7,7)

#indexing element at 4-2 (which is 2)

lst[4-2] # returns 3 (because R indexing starts at 1, not 0)
[1] 3

#BUT indexing element at 2-4 (which is -2) does not work,
#because it means that you are removing the element at index 2, i.e. 3

lst[2-4] #returns the original list without element at index 2
[1] 1 5 6 7 7