s="ABCDEFGHIJKLMNOPQRSTUVWXYZ"*2 for i in range(51):print(s[:-i-1]+s[-i-3::-1],s[:i]+s[i::-1])[26>i]
Standard input is empty
A ABA ABCBA ABCDCBA ABCDEDCBA ABCDEFEDCBA ABCDEFGFEDCBA ABCDEFGHGFEDCBA ABCDEFGHIHGFEDCBA ABCDEFGHIJIHGFEDCBA ABCDEFGHIJKJIHGFEDCBA ABCDEFGHIJKLKJIHGFEDCBA ABCDEFGHIJKLMLKJIHGFEDCBA ABCDEFGHIJKLMNMLKJIHGFEDCBA ABCDEFGHIJKLMNONMLKJIHGFEDCBA ABCDEFGHIJKLMNOPONMLKJIHGFEDCBA ABCDEFGHIJKLMNOPQPONMLKJIHGFEDCBA ABCDEFGHIJKLMNOPQRQPONMLKJIHGFEDCBA ABCDEFGHIJKLMNOPQRSRQPONMLKJIHGFEDCBA ABCDEFGHIJKLMNOPQRSTSRQPONMLKJIHGFEDCBA ABCDEFGHIJKLMNOPQRSTUTSRQPONMLKJIHGFEDCBA ABCDEFGHIJKLMNOPQRSTUVUTSRQPONMLKJIHGFEDCBA ABCDEFGHIJKLMNOPQRSTUVWVUTSRQPONMLKJIHGFEDCBA ABCDEFGHIJKLMNOPQRSTUVWXWVUTSRQPONMLKJIHGFEDCBA ABCDEFGHIJKLMNOPQRSTUVWXYXWVUTSRQPONMLKJIHGFEDCBA ABCDEFGHIJKLMNOPQRSTUVWXYZYXWVUTSRQPONMLKJIHGFEDCBA ABCDEFGHIJKLMNOPQRSTUVWXYXWVUTSRQPONMLKJIHGFEDCBA ABCDEFGHIJKLMNOPQRSTUVWXWVUTSRQPONMLKJIHGFEDCBA ABCDEFGHIJKLMNOPQRSTUVWVUTSRQPONMLKJIHGFEDCBA ABCDEFGHIJKLMNOPQRSTUVUTSRQPONMLKJIHGFEDCBA ABCDEFGHIJKLMNOPQRSTUTSRQPONMLKJIHGFEDCBA ABCDEFGHIJKLMNOPQRSTSRQPONMLKJIHGFEDCBA ABCDEFGHIJKLMNOPQRSRQPONMLKJIHGFEDCBA ABCDEFGHIJKLMNOPQRQPONMLKJIHGFEDCBA ABCDEFGHIJKLMNOPQPONMLKJIHGFEDCBA ABCDEFGHIJKLMNOPONMLKJIHGFEDCBA ABCDEFGHIJKLMNONMLKJIHGFEDCBA ABCDEFGHIJKLMNMLKJIHGFEDCBA ABCDEFGHIJKLMLKJIHGFEDCBA ABCDEFGHIJKLKJIHGFEDCBA ABCDEFGHIJKJIHGFEDCBA ABCDEFGHIJIHGFEDCBA ABCDEFGHIHGFEDCBA ABCDEFGHGFEDCBA ABCDEFGFEDCBA ABCDEFEDCBA ABCDEDCBA ABCDCBA ABCBA ABA A