diff --git a/ChangeLog b/ChangeLog
index 6a96db8..d015231 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,35 @@
+2020-08-27  Christian Barthel  <bch@online.de>
+
+	* lisp/tla+-mode.el (tla+-java-path):
+	(tla+-dot-binary):
+	remove some default paths that may be not useful or
+	helpful for other users.
+	(tla+-run-sany):
+	(tla+-run-model):
+	(tla+-run-pluscal):
+	(tla+-run-tlatex):
+	(tla+-run-model): add an error check (if the
+	tla+-tlatools-path is not set, print an error message)
+	(tla+-run-dot): run dot only when the binary to dot
+	is given.
+
+
+2020-08-03  Christian Barthel  <bch@online.de>
+
+	* org/Test.org: add an example org file.
+	this shows the usage of org-babel-tangle in
+	combination with TLA+ (it may be used to
+	further comment on TLA+ specifications).
+
+	* lisp/tla+-mode.el: update URLs, remove
+	unnecessary comments, cleanup whitespace and
+	wrap lines.
+	(tlc-widget-example): if a TLC cfg already
+	exists, copy it to .old.<seconds>.  erase
+	the buffer then and insert the new TLC
+	config into the buffer.
+	Add the current time to the tlc config.
+
 2020-08-02  Christian Barthel  <bch@online.de>
 
 	* lisp/tla+-mode.el (tla+-tlc-depth): tune depth
diff --git a/lisp/tla+-mode.el b/lisp/tla+-mode.el
index 08577c5..1592232 100644
--- a/lisp/tla+-mode.el
+++ b/lisp/tla+-mode.el
@@ -51,7 +51,7 @@
   :group 'tla+)
 
 (defcustom tla+-tlatools-path
-  "/usr/home/bch/tmp/tlaplus/tlatools/dist/tla2tools_1.6.0.jar"
+  nil
   "Path to the TLA+ `tlatools.jar' toolbox java archive"
   :type 'file
   :group 'tla+)
@@ -117,7 +117,7 @@
   :type 'string)
 
 (defcustom tla+-dot-binary
-  "dot"
+  nil
   "path to dot binary"
   :type 'string)
 
@@ -562,6 +562,8 @@ Operation:
 3. errors are converted into clickable buttons by using the
    `tla+/find-error-marks' function."
   (interactive)
+  (if (not tla+-tlatools-path)
+      (error "need the TLA+ toolbox java archive: tla+-tlatools-path"))
   (let* ((filename (buffer-file-name))
          (sanybuffer
           (get-buffer-create
@@ -582,10 +584,11 @@ Operation:
       (other-window 1))))
 
 (defun tla+-run-dot ()
-  (let ((cmd (format "%s -Tpng states.dot > %s"
-                     tla+-dot-binary
-                     tla+-dot-convert)))
-    (shell-command-to-string cmd)))
+  (if tla+-dot-binary
+      (let ((cmd (format "%s -Tpng states.dot > %s"
+			 tla+-dot-binary
+			 tla+-dot-convert)))
+	(shell-command-to-string cmd))))
 
 (defun tla+-run-model (cfgfile)
   "Run the tlc2.TLC Model checker
@@ -605,6 +608,8 @@ Note: The TLA+ specification file is a relative path.
             (concat
              (file-name-base (buffer-file-name))
              ".cfg" ))))
+  (if (not tla+-tlatools-path)
+      (error "need the TLA+ toolbox java archive: tla+-tlatools-path"))  
   (let* ((filename (buffer-file-name))
          (tlcbufname (format "*tlc2.TLC* [%s]" (buffer-name)))
          ;(tlcbuffer (get-buffer-create
@@ -682,6 +687,9 @@ was not 0), an error message will be printed.
                tla+-java-path " -cp " tla+-tlatools-path
                " pcal.trans "filename ))
          (output (shell-command cmd)))
+    (if (not tla+-tlatools-path)
+	(error
+	 "need the TLA+ toolbox java archive: tla+-tlatools-path"))
     (if (= output 0)
         (progn
           (revert-buffer nil t)
@@ -783,6 +791,9 @@ The function executes one or two shell commands synchronously."
          (convert2ps (concat
                       tla+-dvips-path " " dvipath)))
     (progn
+      (if (not tla+-tlatools-path)
+	  (error
+	   "need the TLA+ toolbox java archive: tla+-tlatools-path"))
       (cond
        ((eq type 'pdf)
         (shell-command convert2pdf))