Smaller things:

- case names for "weak" induction rules (names of the 
constructors); see page 61/62 and 170 in Tutorial

- <type>_perm rules should be added to the simplifier;
  maybe <type>_perm whould be called permute_<type>.simps;
  that would conform with the terminology in Nominal2

- <type>_fv / <type>_bn / <type>_distinct should also be 
  added to the simplifier


Bigger things:

- nested recursion, like types "trm list" in a constructor

- strong induction rules

- show support equations

- automate the proofs that are currently proved with sorry:
  alpha_equivp, fv_rsp, alpha_bn_rsp, alpha_bn_reflp

- store information about defined nominal datatypes, so that
  it can be used to define new types that depend on these

- make 3 versions of Abs

- make parser aware of recursive and of different versions of abs