### diff src/LogicProg.v @ 506:05c0f872a129

Pass through Chapter 13
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```--- a/src/LogicProg.v	Sun Feb 10 15:40:28 2013 -0500
+++ b/src/LogicProg.v	Sun Feb 10 16:00:26 2013 -0500
@@ -126,7 +126,7 @@
apply PlusS.
apply PlusO.

-(** At this point the proof is completed.  It is no doubt clear that a simple procedure could find all proofs of this kind for us.  We are just exploring all possible proof trees, built from the two candidate steps [apply PlusO] and [apply PlusS].  The built-in tactic %\index{tactics!auto}%[auto] does exactly that, since above we used %\index{Vernacular commands!Hint Constructors}%[Hint Constructors] to register the two candidate proof steps as hints. *)
+(** At this point the proof is completed.  It is no doubt clear that a simple procedure could find all proofs of this kind for us.  We are just exploring all possible proof trees, built from the two candidate steps [apply PlusO] and [apply PlusS].  The built-in tactic %\index{tactics!auto}%[auto] follows exactly this strategy, since above we used %\index{Vernacular commands!Hint Constructors}%[Hint Constructors] to register the two candidate proof steps as hints. *)

Restart.
auto.
@@ -813,7 +813,7 @@

(** Let us stop at this point and take stock of the possibilities for [auto] and [eauto] hints.  Hints are contained within _hint databases_, which we have seen extended in many examples so far.  When no hint database is specified, a default database is used.  Hints in the default database are always used by [auto] or [eauto].  The chance to extend hint databases imperatively is important, because, in Ltac programming, we cannot create "global variables" whose values can be extended seamlessly by different modules in different source files.  We have seen the advantages of hints so far, where [crush] can be defined once and for all, while still automatically applying the hints we add throughout developments.  In fact, [crush] is defined in terms of [auto], which explains how we achieve this extensibility.  Other user-defined tactics can take similar advantage of [auto] and [eauto].

-The basic hints for [auto] and [eauto] are: %\index{Vernacular commands!Hint Immediate}%[Hint Immediate lemma], asking to try solving a goal immediately by applying a lemma and discharging any hypotheses with a single proof step each; %\index{Vernacular commands!Hint Resolve}%[Resolve lemma], which does the same but may add new premises that are themselves to be subjects of nested proof search; %\index{Vernacular commands!Hint Constructors}%[Constructors type], which acts like [Resolve] applied to every constructor of an inductive type; and %\index{Vernacular commands!Hint Unfold}%[Unfold ident], which tries unfolding [ident] when it appears at the head of a proof goal.  Each of these [Hint] commands may be used with a suffix, as in [Hint Resolve lemma : my_db].  This adds the hint only to the specified database, so that it would only be used by, for instance, [auto with my_db].  An additional argument to [auto] specifies the maximum depth of proof trees to search in depth-first order, as in [auto 8] or [auto 8 with my_db].  The default depth is 5.
+The basic hints for [auto] and [eauto] are: %\index{Vernacular commands!Hint Immediate}%[Hint Immediate lemma], asking to try solving a goal immediately by applying a lemma and discharging any hypotheses with a single proof step each; %\index{Vernacular commands!Hint Resolve}%[Resolve lemma], which does the same but may add new premises that are themselves to be subjects of nested proof search; %\index{Vernacular commands!Hint Constructors}%[Constructors type], which acts like [Resolve] applied to every constructor of an inductive type; and %\index{Vernacular commands!Hint Unfold}%[Unfold ident], which tries unfolding [ident] when it appears at the head of a proof goal.  Each of these [Hint] commands may be used with a suffix, as in [Hint Resolve lemma : my_db], to add the hint only to the specified database, so that it would only be used by, for instance, [auto with my_db].  An additional argument to [auto] specifies the maximum depth of proof trees to search in depth-first order, as in [auto 8] or [auto 8 with my_db].  The default depth is 5.

All of these [Hint] commands can be expressed with a more primitive hint kind, [Extern].  A few more examples of [Hint Extern] should illustrate more of the possibilities. *)
```