src/Pure/ProofGeneral/pgip.ML

clarified strip_shyps: proper type witnesses for present sorts;
moved fold_terms to thm.ML;

(*  Title:      Pure/ProofGeneral/pgip.ML
    Author:     David Aspinall

Prover-side PGIP abstraction.  
Not too closely tied to Isabelle, to help with reuse/porting.
*)

signature PGIP =
sig
    include PGIPTYPES
    include PGIPMARKUP
    include PGIPINPUT
    include PGIPOUTPUT
end

structure Pgip : PGIP = 
struct
   open PgipTypes
   open PgipMarkup
   open PgipInput
   open PgipOutput
end