getCT
Thm.getCT : unit -> string option
Returns the current theory threaded through Thm's definition
principles, or NONE if none has yet been set.
Thm holds the current-theory name alongside its other state so that
Thm.prim_type_definition, Thm.prim_specification and
Thm.gen_prim_specification can read it without a caller argument.
The value returned here is that name.
At kernel startup the value is NONE; Thm.setCT (invoked from
Theory.new_theory) sets it. Until then the definition principles
raise.
Failure
Never fails.