递归模板 2 多条件

 (defun fn (x)
      (cond (test-condition1 the-value1)
            (test-condition2 the-value2)
            ...
            ...
            ...
            (t (fn reduced-argument-x))))

 CL-USER 2788 > (defun my-fib (n)
                 (cond ((= n 1) 1)
                       ((= n 2) 1)
                       (t (+
                           (my-fib (- n 1))
                           (my-fib (- n 2))))))
MY-FIB

CL-USER 2789 > (my-fib 1)
1

CL-USER 2790 > (my-fib 2)
1

CL-USER 2791 > (my-fib 3)
2

CL-USER 2792 > (my-fib 4)
3

CL-USER 2793 > (my-fib 5)
5

CL-USER 2794 > (my-fib 6)
8

CL-USER 2795 > (my-fib 7)
13