Immutable Source of Mutable Instances
The Keykos factory is immutable and can thus be shared between
regimes that are not allowed to communicate.
That same factory may produce mutable objects to solve
all sorts of pratical problems.
The code that defines these mutable objects need not be examined
to ensure the above communication property.
The Java patterns for creating new objects fail to match this pattern
for sibling objects may share static mutable variables.
Access to the source, or perhaps bytecodes, is necessary to ensure
that this is not the case.
We need a precise definition of "immutable".