A verified resolution checker
Matt Kaufmann and Sol Swords (see each book's header for authorship)

This checker was used at Centaur Technology for checking resolution
proofs.  The file zz.lisp has been modified, however, because the
backend (SAT solver etc.) is not included here.

These books give an example of how to set up two-pass certification
with SAT solving and proof recording in the first pass and proof
checking without ttags in the second pass.  The top-level book of
these is zz-two-pass.lisp.  The way to use it in a certified book is
to first invoke (zz-two-pass-start), do whatever events use SAT
solving (using e.g.  zzv-sat or zzv-batch-sat), and call
(zz-two-pass-stop) at the end of the book.
