Added a few exports
Merge branch 'master' of github.com:samowre/PVS
Modified subtype-preds (subtype subtype) to use (compatible-type t2 t1) rather
than just t2 in going up the supertype, as it could jump past, e.g.,
A st B st C, and supertype(A) = C causes problems.
Merge branch 'master' of github.com:samowre/PVS