4 files changed, 59 insertions, 1 deletions
diff --git a/theories/FSets/DecidableType.v b/theories/FSets/DecidableType.v
index 4e34bbc0d..a4de6ca7f 100644
--- a/theories/FSets/DecidableType.v
+++ b/theories/FSets/DecidableType.v
@@ -31,6 +31,7 @@ Module Type DecidableType.
 
 End DecidableType. 
 
+(** * Additional notions about keys and datas used in FMap *)
 
 Module KeyDecidableType(D:DecidableType).
  Import D.
@@ -147,5 +148,9 @@ Module KeyDecidableType(D:DecidableType).
  Hint Unfold MapsTo In.
  Hint Resolve In_inv_2 In_inv_3.
 
-
 End KeyDecidableType.
+
+
+
+
+
diff --git a/theories/FSets/DecidableTypeEx.v b/theories/FSets/DecidableTypeEx.v
new file mode 100644
index 000000000..dcca37095
--- /dev/null
+++ b/theories/FSets/DecidableTypeEx.v
@@ -0,0 +1,50 @@
+(***********************************************************************)
+(*  v      *   The Coq Proof Assistant  /  The Coq Development Team    *)
+(* <O___,, *        INRIA-Rocquencourt  &  LRI-CNRS-Orsay              *)
+(*   \VV/  *************************************************************)
+(*    //   *      This file is distributed under the terms of the      *)
+(*         *       GNU Lesser General Public License Version 2.1       *)
+(***********************************************************************)
+
+(* $Id$ *)
+
+Require Import DecidableType OrderedType OrderedTypeEx.
+Set Implicit Arguments.
+Unset Strict Implicit.
+
+(** * Examples of Decidable Type structures. *)
+
+(** A particular case of [DecidableType] where 
+    the equality is the usual one of Coq. *)
+
+Module Type UsualDecidableType.
+ Parameter t : Set.
+ Definition eq := @eq t.
+ Definition eq_refl := @refl_equal t.
+ Definition eq_sym := @sym_eq t.
+ Definition eq_trans := @trans_eq t.
+ Parameter eq_dec : forall x y, { eq x y }+{~eq x y }.
+End UsualDecidableType.
+
+(** a [UsualDecidableType] is in particular an [DecidableType]. *)
+
+Module UDT_to_DT (U:UsualDecidableType) <: DecidableType := U.
+
+(** An OrderedType can be seen as a DecidableType *)
+
+Module OT_as_DT (O:OrderedType) <: DecidableType. 
+ Module OF := OrderedTypeFacts O.
+ Definition t := O.t.
+ Definition eq := O.eq. 
+ Definition eq_refl := O.eq_refl. 
+ Definition eq_sym := O.eq_sym. 
+ Definition eq_trans := O.eq_trans. 
+ Definition eq_dec := OF.eq_dec. 
+End OT_as_DT.
+
+(** (Usual) Decidable Type for [nat], [positive], [N], [Z] *)
+
+Module Nat_as_DT <: UsualDecidableType := OT_as_DT (Nat_as_OT).
+Module Positive_as_DT <: UsualDecidableType := OT_as_DT (Positive_as_OT).
+Module N_as_DT <: UsualDecidableType := OT_as_DT (N_as_OT).
+Module Z_as_DT <: UsualDecidableType := OT_as_DT (Z_as_OT).
diff --git a/theories/FSets/FMapWeak.v b/theories/FSets/FMapWeak.v
index 7baeb2970..7bdee004e 100644
--- a/theories/FSets/FMapWeak.v
+++ b/theories/FSets/FMapWeak.v
@@ -8,5 +8,7 @@
 
 (* $Id$ *)
 
+Require Export DecidableType.
+Require Export DecidableTypeEx.
 Require Export FMapWeakInterface.
 Require Export FMapWeakList.
diff --git a/theories/FSets/FSetWeak.v b/theories/FSets/FSetWeak.v
index ccf590ca3..8631841fb 100644
--- a/theories/FSets/FSetWeak.v
+++ b/theories/FSets/FSetWeak.v
@@ -9,6 +9,7 @@
 (* $Id$ *)
 
 Require Export DecidableType.
+Require Export DecidableTypeEx.
 Require Export FSetWeakInterface.
 Require Export FSetFacts.
 Require Export FSetProperties.