ACL2 Seminar, Feb. 23, 2011 A Datatype Manager for ACL2 -- A Work in Progress J Strother Moore Abstract: Even though ACL2 is an untyped language most systems of functions implicitly rely on list structured ``data types.'' I will report on my recent work to support a succinct language to declaring such ``types'' and for supporting reasoning about such types. The basic approach is straightforward: use type definitions and declared signatures to generate ordinary lemmas proved by ordinary ACL2 means and stored as ordinary ACL2 rules. Perhaps the most interesting thing about the whole project is the perspective that it is an initial prototype at a far grander idea: the automatic management of rules and rule classes. This is a work in progress and the system as implemented so far is far from ready for other users.