A palindrome is a string that is the same when reversed. For example, "abba" is a palindrome. Here is a math-like definition: palindrome ("") = true palindrome ( x ) = true palindrome (x+x+y) = false, if x != y = palindrome ( X ), if x == y The symbol x stands for a single character, as does y. The symbol X stands for a string of characters. The symbol + stands for concatenation. Implement palindrome () and a program that tests it.