  Information systems with witnesses have been introduced in [D. Spreen.
Generalised information systems capture L-domains. arXiv:1610.02260v2] as a
logic-style representation of L-domains: The category of such information
systems with approximable mappings as morphisms is equivalent to the category
of L-domains with Scott continuous functions, which is known to be Cartesian
closed. In the present paper a direct proof of the Cartesian closure of the
category of information systems with witnesses and approximable mapppings is
given. As is shown, the collection of approximable mappings between two
information systems with witnesses comes with a natural information system
structure.
