-----Description-----
This task requires writing a Lean 4 method that checks whether a given string is a palindrome. A palindrome is a string that reads the same forwards and backwards. The function should ignore whitespace, punctuation, and capitalization when checking for palindromes.

-----Input-----
The input consists of:
s: A string to be checked.

-----Output-----
The output is a boolean:
Returns true if the input string is a palindrome when non-alphabetic characters are removed and letters are treated case-insensitively, and false otherwise.

