NOTE:When there are no registered visualisation clients, this predicate fails with all arguments, and has no effect.
If ViewableName is the name of an existent viewable,
        Type is unified with its type. See
        viewable_create/3 for a discussion of valid viewable
        types.
[Assuming that at least one visualisation client is registered]
	Success:
	viewable_create(v1, []([](R,S), [](Q,W)), 
			array([fixed, fixed], any)), 
	viewable_type(v1, X).
        [gives X = array([fixed, fixed], any)]
	Failure:
	viewable_create(v1, []([](R,S), [](Q,W)), 
		array([fixed, fixed], any)), 
	viewable_type(v1, q).
	Exceptions raised:
	viewable_create(v1, []([](R,S), [](Q,W)), 
		array([fixed, fixed], any)), 
	viewable_type(123, _).
        [gives error 4]