diff --git a/ex-5_07-13.scm b/ex-5_07-13.scm
index c18683c..8fb2d55 100644
--- a/ex-5_07-13.scm
+++ b/ex-5_07-13.scm
@@ -357,6 +357,14 @@
 (display "[ok]\n")
 
 (display "\nex-5.13 - dynamic-registers\n")
-;; (load "misc/sicp-regsim.scm")
 
-(display "TBD!\n")
+(define (lookup-register name)
+  (let ((val (assoc name register-table)))
+    (if val
+        (cadr val)
+        (begin  ;; Allocate register dynamically if needed
+          (allocate-register name)
+          (lookup-register name)))))
+
+(display "[ok]\n")
+
diff --git a/ex-5_14-xx.scm b/ex-5_14-xx.scm
index aeb2cdb..218b3e1 100644
--- a/ex-5_14-xx.scm
+++ b/ex-5_14-xx.scm
@@ -1,6 +1,49 @@
 (load "util.scm")
 (load "misc/sicp-regsim.scm")
 
-(display "\nex-5.14\n")
+(display "\nex-5.14 - factorial-stack-evaluation\n")
 
-(display "\nex-5.15\n")
+(define factorial-machine (make-machine
+  '(n val continue)
+  (list (list '= =) (list '- -) (list '* *))
+  '(controller
+     (assign continue (label fact-done))     ; set up final return address
+   fact-loop
+     (test (op =) (reg n) (const 1))
+     (branch (label base-case))
+     ;; Set up for the recursive call by saving n and continue.
+     ;; Set up continue so that the computation will continue
+     ;; at after-fact when the subroutine returns.
+     (save continue)
+     (save n)
+     (assign n (op -) (reg n) (const 1))
+     (assign continue (label after-fact))
+     (goto (label fact-loop))
+   after-fact
+     (restore n)
+     (restore continue)
+     (assign val (op *) (reg n) (reg val))   ; val now contains n(n - 1)!
+     (goto (reg continue))                   ; return to caller
+   base-case
+     (assign val (const 1))                  ; base case: 1! = 1
+     (goto (reg continue))                   ; return to caller
+   fact-done)))
+
+(define (run-machine-for n)
+  (display "factorial ") (display n)
+  ((factorial-machine 'stack) 'initialize)
+  (set-register-contents! factorial-machine 'n n)
+  (start factorial-machine)
+  ; (assert (get-register-contents factorial-machine 'val) 720)
+  ((factorial-machine 'stack) 'print-statistics)
+  (newline))
+
+(map run-machine-for '(10))
+
+; For each recursion there are two pushes and there are (n - 1) recursions.
+; total-pushes(n) = (n - 1) * 2
+; max-depth: (n - 1) * 2
+
+(display "\nex-5.15 - instruction-counting\n")
+
+(display "\nex-5.16\n")