Помощ със задачата Mock Exam 4 Title Search Python

output = []

str2 = 'No such title found!'

def convert(s):
    str1 = ""
    return(str1.join(s))

def split(word):
	return list(word)

let_t = split(input())

n = int(input())

for i in range(n):

    str_i = split(input())

    for j in range(len(str_i)):

        if str_i[j] in let_t:

            let_t.index(str_i[j])

            x = let_t.index(str_i[j])

            let_t.remove(let_t[x])

    k = convert(let_t)

    output.append(k)

    print(output)