Please use Recursion

This is a C++ problem, thank you for your help.

IS AN INPUT STRING A PALINDROME? A palindrome is a string in which the letters are the same in both directions, disregarding capitalization and non-letter characters. Write a program that reads a sequence of characters and calls a recursive Boolean function to determine if the letters in the string form a palindrome. Several runs of this program might look like this: csh> pal Enter a line that might be a palindrome: Madam I'm Adam. This string IS a palindrome csh> pal Enter a line that might be a palindrome: Able was I ere I saw Elba. This string IS a palindrome. csh> pal Enter a line that might be a palindrome: Go hang a salami, T'm a lasagna hog. This string IS a palindrome. csh> pal Enter a line that might be a palindrome This is another candidate string. This string is NOT a palindrome. This string iS NOT a palindrome This problem is much easier if the input is read one character at a time, all non-letters are eliminated during input, and all letters are converted to one case Also note that a string containing no letters IS a palindrome Hint: Work from both ends of the sequence of letters