Problem
Write in SML program of problems shown using pattern style.
A. Write a function remvdub to remove duplicate of elements from a lists. remvdub(["a","b", "a", "c", "b", "a", "c"]) > ["a", "b", "c"].
B. Write a function to display n-th character of a string. You may assume that input is always longer than n. dispnthc("abcdef", 4) > #"d"
C. Write a function remv to remove elements from a list(including all multiple appearances). remv(["a", ["a", "b", "a", "c"]) > ["b", "c"].