def fib(n):
    '''Return the nth fibonacci number.'''
    if n == 0 or n == 1:
        return 1
    else:
        return fib(n - 1) + fib(n - 2)
    
    
def strlen(some_string):
    '''Recursively return the length of some_string.'''
    if some_string == '':
        return 0
    else:
        return 1 + strlen(some_string[1:])    
    
    
def reverse(s):
    '''Return the string s in reverse.'''
    if s == '':
        return ''
    else:
        return reverse(s[1:]) + s[0]


def is_palindrome(s):
    '''Return whether s is a palindrome.'''
    if len(s) <= 1:
        return True
    elif s[0] != s[-1]:
        return False
    else:
        # recursive case
        return is_palindrome(s[1:-1])


def contains_pattern(text, pattern):
    '''Return whether pattern appears somewhere in text.'''
    if text.startswith(pattern):
        return True
    elif len(pattern) > len(text):
        return False
    else:
        return contains_pattern(text[1:], pattern)