update

doc/src/sketcher/sketcher.do.txt

@@ -305,7 +305,7 @@ You can try this by running the present example in the file
 # #ifdef PRIMER_BOOK
 `vehicle0.py`.
 # #else
-"`vehicle0.py`": "http://hplgit.github.com/pysketcher/doc/src/sketcher/sketcher.do.txt".
+"`vehicle0.py`": "http://hplgit.github.com/pysketcher/doc/src/sketcher/src-sketcher/vehicle0.py", or view a ready-made "movie": "http://hplgit.github.com/pysketcher/doc/src/sketcher/src-sketcher/vehicle0_animation/anim.html".
 # #endif
 
 === Animation: Rolling the Wheels ===
@@ -370,8 +370,12 @@ def move_vehicle(t, fig):
     w2 = fig['vehicle']['wheels']['wheel2']
     w2.rotate(degrees(angle), center=(wheel1_center+4, R))
 !ec
-
-
+The complete example is found in the file
+# #ifdef PRIMER_BOOK
+`vehicle1.py`.
+# #else
+"`vehicle1.py`": "http://hplgit.github.com/pysketcher/doc/src/sketcher/src-sketcher/vehicle0.py". You may run this file or watch a "ready-made movie": "http://hplgit.github.com/pysketcher/doc/src/sketcher/src-sketcher/vehicle0_animation/anim.html".
+# #endif
 
 The great advantage with making figures this way through programming,
 rather than using interactive drawing programs, is that the
@@ -380,7 +384,11 @@ can be parameterized through variables such that the
 proportions of parts of the figure can be quickly changed,
 groups of objects can easily be manipulated (translated, rotated,
 scaled), objects can be left out while experimenting with the
-figure, to mention some important features.
+figure, to mention some important features. However, the single
+most important feature is the ability to make animations governed
+by mathematical formulas, maybe coming from simulations
+based on solving differential equations reflecting the physics
+of the problem.