Mututal recursion from wikipedia

is_even_odd

# http://en.wikipedia.org/wiki/Mutual_recursion

bool is_even(unsigned int n)
    if (n == 0)
        return true;
    else
        return is_odd(n - 1);
 
bool is_odd(unsigned int n)
    if (n == 0)
        return false;
    else
        return is_even(n - 1);