Prolog in Scheme is a collection of macros that expand syntax for
   clauses, elations, and so on. It is written in Scheme and has support
   for delayed goals and interval arithmetic. It is known to run in Chez
   Scheme and in Elk, and is intended to be portable to other Scheme
   implementations. It relies on continuations, and so is not easily
   ported to Common Lisp. Available from the University of Calgary by
   anonymous ftp from
      ftp.cpsc.ucalgary.ca:/pub/projects/prolog1.2/prolog12.tar.Z
   Questions and comments may be addressed to Alan Dewar
   <dewar@cpsc.ucalgary.ca> or John Cleary <jcleary@waikato.ac.nz>.

   Schelog is an embedding of Prolog in Scheme. It represents Prolog
   goals as procedures in Scheme, and includes macros to simulate a
   Prolog-style syntax for clauses, relations and queries.  The embedding
   permits the user to combine Prolog and Scheme code freely, in the same
   s-expression, if desired.  Documentation and examples are included.
   Schelog should run in any R4RS Scheme, has been tested in SCM and Chez
   Scheme, and will run in any Scheme implementation that supports SLIB (see
   entry in [1-10] above).  Schelog (version 2) is available by anonymous
   ftp from titan.cs.rice.edu:/public/dorai/schelog2.tar.Z.  Its use of
   higher-order continuations is probably a major obstacle to porting it
   to Common Lisp.  For more information, please contact the author Dorai
   Sitaram <dorai@cs.rice.edu>.