2014-05-06: much stronger tests.

much stronger tests.

diff --git a/examples/d20world.w b/examples/d20world.w
--- a/examples/d20world.w
+++ b/examples/d20world.w
@@ -216,6 +216,30 @@ format #t "Advect ~A\n" 0.1
 d20-advect world advection-directions 0.1
 display : d20-as-text world
 newline
+format #t "Advect: ~A*(~A)\n" 1000 0.001
+let loop : : steps 1000
+    cond
+      : = 0 steps
+        . world
+      else
+        d20-advect world advection-directions 0.001
+        display : d20-as-text world
+        d20-cursor-up-text world
+        loop : 1- steps
+display : d20-as-text world
+newline
+format #t "Diffuse: ~A*(~A)\n" 1000 0.004
+let loop : : steps 1000
+    cond
+      : = 0 steps
+        . world
+      else
+        d20-diffuse world neighbors 0.004
+        display : d20-as-text world
+        d20-cursor-up-text world
+        loop : 1- steps
+display : d20-as-text world
+newline
 format #t "Diffuse+Advect: ~A*(~A+~A)\n" 10000 0.002 0.001
 let loop : : steps 10000
     cond