unpaintable (the solution to logical const)

[Knud Soerensen]

> Walter said that having mutable fields breaks the whole const system.
> He may have been right - but having /unpaintable/ fields is just fine
> and dandy. Everything works. const(...) and invariant(...) will paint
> only the paintable fields with constancy, but those fields the paint
> recursively.
> 
> It just works.

I like the idea. Here are some suggestion for a better name.
isolate
confine
detach
stable
steady
stationary
fixed
permanent