Renamed sum_case to basic_sum_case.
(*  Title:      HOL/SVC_Oracle.ML
    ID:         $Id$
    Author:     Lawrence C Paulson
    Copyright   1999  University of Cambridge
Installing the oracle for SVC (Stanford Validity Checker)
Based upon the work of Søren T. Heilmann
*)
(*Present the entire subgoal to the oracle, assumptions and all, but possibly
  abstracted.  Use via compose_tac, which performs no lifting but will
  instantiate variables.*)
local val svc_thy = the_context () in
fun svc_tac i st = 
  let val prem = BasisLibrary.List.nth (prems_of st, i-1)
      val th = invoke_oracle svc_thy "svc_oracle"
	             (#sign (rep_thm st), Svc.OracleExn prem)
   in 
      compose_tac (false, th, 0) i st
   end 
   handle Svc.OracleExn _ => Seq.empty
	| Subscript       => Seq.empty;
end;
(*True if SVC appears to exist*)
fun svc_enabled() = getenv "SVC_HOME" <> "";