Write a function which takes in a list lst, an argument entry, and another argument elem. This function will check through each item present in lst to see if it is equivalent with entry. Upon finding an equivalent entry, the function should modify the list by placing elem into the list right after the found entry. At the end of the function, the modified list should be returned. See the doctests for examples on how this function is utilized. Use list mutation to modify the original list, no new lists should be created or returned.