
See the works of:
<ul>
<li>_(Solomon Feferman | http://math.Stanford.EDU/~feferman/) did a lot of work.
<li>Raymond Smullyan
<li>_(John Harrison's review | http://portal.acm.org/citation.cfm?id=235792&coll=portal&dl=ACM&CFID=11111111&CFTOKEN=2222222)?
<li>_(NuPrl)
<li>_(Jos Meseguer | http://www.cs.uiuc.edu/people/faculty/meseguer.html) headed the _(Rewriting Project | ) at SRI, resulting mainly in _(Maude). See also _(Semantic Foundations for Compositions | http://www.darpa.mil/ito/psum1997/D898-0.html).
<li>_(Samuel Boutin | http://pauillac.inria.fr/~boutin/) wrote a PhD thesis on reflection and quotients in _(Higher-Order Logic)s.
<li>_(R.B. Jones' | http://www.rbjones.com) _(page on logic | http://www.rbjones.com/rbjpub/logic/)
<li>_(Aurlien Slodzian | http://arti.vub.ac.be/~as/)'s paper on _(knowledge-level reflection | http://arti.vub.ac.be/~as/papers/kl-reflection/kl-reflection.html).
</ul>