You may obtain a copy of the prototype refinement checker via cvs with

  cvs -d :pserver:guest_sorts@cvs.concert.cs.cmu.edu:/cvsroot login
  (empty password)
  cvs -d :pserver:guest_sorts@cvs.concert.cs.cmu.edu:/cvsroot checkout ssml
  cd ssml

and update it with (while in the ssml directory):

  cvs update -d

Follow the brief instructions in ssml/README-REFINEMENTS.  One thing to keep in
mind that you will need SML of NJ version 110.0.7 (see instructions, or get it
from http://www.smlnj.org)

The example in test-ssml/fp-examples/norm.sml was one of the early motivating
examples, because in the Twelf implementation many functions rely on weak
head-normal forms and similar invariants.  What is checked there is that
normlization returns a normal form (and weak head-normalization returns a weak
head-normal form).

The implementation is as a conservative extension of SML, so you can run your
code with

  - use "file.sml";

and refinement check it with

  - R.refine_file "file.sml";