removed reference to Nat thms in elim_rls.

Minor mod.

Polished proofs.

Improving space efficiency of inductive/datatype definitions. Reduce usage of "open" and change struct open X; D end to let open X in struct D end end whenever possible -- removes X from the final structure. Especially needed for functors Intr_elim and Indrule.

Modified non-empty-types warning in HOL.

Reduced indentation; no change in function

Purely cosmetic changes