let palindrome s =
        let s = toUpper s
        let rec palindrome (s:string) acc =
                match s with
                | x when not (Char.IsLetter(x.[acc]) && Char.IsLetter(x.[0])) -> if Char.IsLetter(x.[0]) then (palindrome (s.Substring(0,acc-1)) acc-1) else (palindrome (s.Substring(1,acc)) acc-1)
                | x when acc > 1 -> if (s.[acc] = s.[0]) then (palindrome (s.Substring(1,acc-1)) acc-1) else false
                | _ -> true
        palindrome s (s.Length-1)