--- a/src/Pure/Isar/proof_history.ML Wed Jul 13 16:07:35 2005 +0200
+++ b/src/Pure/Isar/proof_history.ML Wed Jul 13 16:07:36 2005 +0200
@@ -13,6 +13,7 @@
val init: int option -> Proof.state -> T
val is_initial: T -> bool
val current: T -> Proof.state
+ val previous: T -> Proof.state option
val clear: int -> T -> T
val undo: T -> T
val redo: T -> T
@@ -48,6 +49,7 @@
fun init lim st = ProofHistory (History.init lim ((st, Seq.empty), []));
fun is_initial (ProofHistory prf) = History.is_initial prf;
fun current (ProofHistory prf) = fst (fst (History.current prf));
+fun previous (ProofHistory prf) = Option.map (fst o fst) (History.previous prf);
val clear = app o History.clear;
val undo = app History.undo;
val redo = app History.redo;