classDB.datatype class
Datatype for classifying theory elements.
Many of the functions in the DB structure return answers
that involve the class type, which is declared as
datatype class = Thm | Axm | Def
When occurring with th, an ML value of type
thm, Axm means that th has been
asserted as an axiom; Def means that th is a
constant definition; and Thm means that th is
a plain old theorem, i.e,. not an axiom or a definition.