HOL Light uses ``pretypes'' and ``preterms'' as intermediate structures for
parsing and typechecking, which are later converted to types and terms. A call
preterm_of_term `tm` converts in the other direction, from a normal HOL term
back to a preterm.
FAILURE CONDITIONS
Never fails.
USES
User manipulation of pretypes is not usually necessary, unless you seek to
radically change aspects of parsing and typechecking.