gracefully handle types like 'enat' whose coinductive view is registered using 'free_constructors'
gracefully handle types like 'enat' whose coinductive view is registered using 'free_constructors'

MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle