Solution exercises from P01 to P07

p07.el

@@ -0,0 +1,10 @@
+;; P07 (**) Flatten a nested list structure.
+(defun my-flatten (l)
+  (cond
+   ((null l) nil)
+   ((atom l) (list l))
+   (t
+    (append (my-flatten (car l))
+	    (my-flatten (cdr l))))))
+
+(my-flatten '(a (b (c d) e))) ; '(a b c d e)