had written, in the margin, so many years ago:

| brain, skin, shell -&gt; ectoderm
|
| cortex, cork, bark -&gt; epi-\
|                            &gt; Derm
| keratin, horn, ... -&gt; exo-/

Brain as Shell -- it explains a lot!

&gt; Physics has just refined and formalized (i.e.,
&gt; symbolically represented) this distinction.
&gt; Things that change are called &quot;observers&quot;
&gt; and &quot;initial conditions&quot;, ...

I call these &quot;boundaries&quot;.

&gt; ... things that do not change are c