diff -r bf085daea304 -r bee83c9d3306 src/HOL/ex/Iff_Oracle.thy
--- a/src/HOL/ex/Iff_Oracle.thy	Mon Jun 08 21:38:41 2020 +0200
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,78 +0,0 @@
-(*  Title:      HOL/ex/Iff_Oracle.thy
-    Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
-    Author:     Makarius
-*)
-
-section \<open>Example of Declaring an Oracle\<close>
-
-theory Iff_Oracle
-imports Main
-begin
-
-subsection \<open>Oracle declaration\<close>
-
-text \<open>
-  This oracle makes tautologies of the form \<^prop>\<open>P \<longleftrightarrow> P \<longleftrightarrow> P \<longleftrightarrow> P\<close>.
-  The length is specified by an integer, which is checked to be even
-  and positive.
-\<close>
-
-oracle iff_oracle = \<open>
-  let
-    fun mk_iff 1 = Var (("P", 0), \<^typ>\<open>bool\<close>)
-      | mk_iff n = HOLogic.mk_eq (Var (("P", 0), \<^typ>\<open>bool\<close>), mk_iff (n - 1));
-  in
-    fn (thy, n) =>
-      if n > 0 andalso n mod 2 = 0
-      then Thm.global_cterm_of thy (HOLogic.mk_Trueprop (mk_iff n))
-      else raise Fail ("iff_oracle: " ^ string_of_int n)
-  end
-\<close>
-
-
-subsection \<open>Oracle as low-level rule\<close>
-
-ML \<open>iff_oracle (\<^theory>, 2)\<close>
-ML \<open>iff_oracle (\<^theory>, 10)\<close>
-
-ML \<open>
-  \<^assert> (map (#1 o #1) (Thm_Deps.all_oracles [iff_oracle (\<^theory>, 10)]) = [\<^oracle_name>\<open>iff_oracle\<close>]);
-\<close>
-
-text \<open>These oracle calls had better fail.\<close>
-
-ML \<open>
-  (iff_oracle (\<^theory>, 5); error "Bad oracle")
-    handle Fail _ => writeln "Oracle failed, as expected"
-\<close>
-
-ML \<open>
-  (iff_oracle (\<^theory>, 1); error "Bad oracle")
-    handle Fail _ => writeln "Oracle failed, as expected"
-\<close>
-
-
-subsection \<open>Oracle as proof method\<close>
-
-method_setup iff =
-  \<open>Scan.lift Parse.nat >> (fn n => fn ctxt =>
-    SIMPLE_METHOD
-      (HEADGOAL (resolve_tac ctxt [iff_oracle (Proof_Context.theory_of ctxt, n)])
-        handle Fail _ => no_tac))\<close>
-
-
-lemma "A \<longleftrightarrow> A"
-  by (iff 2)
-
-lemma "A \<longleftrightarrow> A \<longleftrightarrow> A \<longleftrightarrow> A \<longleftrightarrow> A \<longleftrightarrow> A \<longleftrightarrow> A \<longleftrightarrow> A \<longleftrightarrow> A \<longleftrightarrow> A"
-  by (iff 10)
-
-lemma "A \<longleftrightarrow> A \<longleftrightarrow> A \<longleftrightarrow> A \<longleftrightarrow> A"
-  apply (iff 5)?
-  oops
-
-lemma A
-  apply (iff 1)?
-  oops
-
-end