diff --git a/index/alire-index-alire.ads b/index/alire-index-alire.ads
index 3b5b097b..1bc3a83f 100644
--- a/index/alire-index-alire.ads
+++ b/index/alire-index-alire.ads
@@ -27,11 +27,19 @@ package Alire.Index.Alire is
 
                           Dependencies =>
                             Current ("half_life_3") and -- unconditional
-                            If_Platform -- conditional
+                            On_Condition                -- conditional
                               (System_Is (GNU_Linux),
                                When_True => At_Least ("elite_horizons", V ("2.0")) and
                                             At_Least ("star_citizen", V ("3.0")), -- Wish...
-                               When_False => At_Least ("windows_100", V ("1.0"))),
+                               When_False => At_Least ("windows_100", V ("1.0"))) and
+                            When_Available -- Chained preferences
+                              (Preferred => Within_Major ("alire", V ("1.0")),
+                               Otherwise => Within_Major ("alire", V ("0.0"))) and
+                          When_Available -- Chained preferences
+                            (Preferred => Within_Major ("alire", V ("2.0")),
+                             Otherwise => When_Available -- Chained preferences multi-level
+                                            (Preferred => Within_Major ("alire_alt", V ("1.0")),
+                                             Otherwise => Within_Major ("alire", V ("0.5")))),
 
                           Properties   =>
                             GPR_Extra_Config ("-XProfile=False") and
@@ -41,26 +49,26 @@ package Alire.Index.Alire is
                             GPR_Free_Scenario ("Path_To_Something") and
                             --  Known scenario variables
 
-                            If_Platform
+                            On_Condition
                               (System_Is (Windows),
                                GPR_File ("project_win.gpr")) and
-                            If_Platform
+                            On_Condition
                               (System_Is (GNU_Linux),
-                               If_Platform (Distribution_Is (Ubuntu), -- Nested conditions
+                               On_Condition (Distribution_Is (Ubuntu), -- Nested conditions
                                             GPR_File ("project_ubuntu.gpr"))) and
                             --  Conditional project file
 
-                            If_Platform
+                            On_Condition
                               (System_Is (GNU_Linux),
                                Comment ("Long life the penguin")) and
                             --  Conditions on operating system
 
-                            If_Platform
+                            On_Condition
                               (not Compiler_Is (GNAT_Unknown),
                                Comment ("Never saw that compiler") and Comment ("But I would like to")) and
                             --  Conditions on compiler version
 
-                            If_Platform
+                            On_Condition
                               (Version_Is (Ubuntu_Artful),
                                When_True  => Comment ("Living on the edge"),
                                When_False => Comment ("I am a rock")) and
diff --git a/index/alire-index-dak.ads b/index/alire-index-dak.ads
index 09e188ed..ded7ee03 100644
--- a/index/alire-index-dak.ads
+++ b/index/alire-index-dak.ads
@@ -231,36 +231,36 @@ package Alire.Index.DAK is
                                                      );
 
    Components_ODBC_V_4_27 : constant Release :=
-                                            Register (Base & "components_odbc",
-                                                      V ("4.27"),
-                                                      Desc_Pre & "(ODBC bindings)" & Desc_Post,
-                                                      Git (Repo, "47337f8a5dd69404087129d5cca79885d6e8cd3f"),
-                                                      Dependencies =>
-                                                        Within_Major (Components_V_4_27) and
-                                                        Current (UnixODBC.V_2_3),
+                              Register (Base & "components_odbc",
+                                        V ("4.27"),
+                                        Desc_Pre & "(ODBC bindings)" & Desc_Post,
+                                        Git (Repo, "47337f8a5dd69404087129d5cca79885d6e8cd3f"),
+                                        Dependencies =>
+                                          Within_Major (Components_V_4_27) and
+                                          Current (UnixODBC.V_2_3),
 
-                                                      Properties   =>
-                                                        GPR_File ("components-odbc.gpr") and
-                                                        GPR_File ("test_components" / "components-odbc-odbc_bindings_tests.gpr") and
+                                        Properties   =>
+                                          GPR_File ("components-odbc.gpr") and
+                                          GPR_File ("test_components" / "components-odbc-odbc_bindings_tests.gpr") and
 
-                                                        If_Platform
-                                                          (System_Is (GNU_Linux),
-                                                           GPR_Extra_Config ("-Xodbc=unixODBC")) and
-                                                        If_Platform
-                                                          (System_Is (Windows),
-                                                           GPR_Extra_Config ("-Xodbc=ODBC32")) and
-                                                        If_Platform
-                                                          (Word_Size_Is (Bits_32),
-                                                           GPR_Extra_Config ("-Xarch=i686")) and
-                                                        If_Platform
-                                                          (Word_Size_Is (Bits_64),
-                                                           GPR_Extra_Config ("-Xarch=x86_64")) and
+                                          On_Condition
+                                            (System_Is (GNU_Linux),
+                                             GPR_Extra_Config ("-Xodbc=unixODBC")) and
+                                          On_Condition
+                                            (System_Is (Windows),
+                                             GPR_Extra_Config ("-Xodbc=ODBC32")) and
+                                          On_Condition
+                                            (Word_Size_Is (Bits_32),
+                                             GPR_Extra_Config ("-Xarch=i686")) and
+                                          On_Condition
+                                            (Word_Size_Is (Bits_64),
+                                             GPR_Extra_Config ("-Xarch=x86_64")) and
 
-                                                        Executable ("test_odbc_bindings") and
+                                          Executable ("test_odbc_bindings") and
 
-                                                        License  (GMGPL_2_0) and
-                                                        Author   (DAK_Author) and
-                                                        Website  (DAK_Website)
-                                                     );
+                                          License  (GMGPL_2_0) and
+                                          Author   (DAK_Author) and
+                                          Website  (DAK_Website)
+                                       );
 
 end Alire.Index.DAK;
diff --git a/index/alire-index-libadacrypt.ads b/index/alire-index-libadacrypt.ads
index a8afaae2..6a7882f3 100644
--- a/index/alire-index-libadacrypt.ads
+++ b/index/alire-index-libadacrypt.ads
@@ -11,6 +11,7 @@ package Alire.Index.Libadacrypt is
                          V ("0.8.7"),
                          Prj_Desc,
                          Git (Prj_Repo, "06b4907c6ae6dcdce62339ff8fd2913d7bbbc0d9"),
+
                          Properties =>
                            Author     (Prj_Author) and
 
diff --git a/src/alire-conditional.ads b/src/alire-conditional.ads
index 14e2794b..ad4783e8 100644
--- a/src/alire-conditional.ads
+++ b/src/alire-conditional.ads
@@ -6,11 +6,13 @@ with Alire.Requisites;
 package Alire.Conditional with Preelaborate is
 
    package For_Dependencies is new Conditional_Values (Dependencies.Vectors.Vector,
-                                                       Dependencies.Vectors."and");
+                                                       Dependencies.Vectors."and",
+                                                       Dependencies.Vectors.Image_One_Line);
    subtype Dependencies is For_Dependencies.Conditional_Value;
 
    package For_Properties is new Conditional_Values (Properties.Vector,
-                                                     Properties."and");
+                                                     Properties."and",
+                                                     Properties.Image_One_Line);
    subtype Properties is For_Properties.Conditional_Value;
 
 end Alire.Conditional;
diff --git a/src/alire-conditional_values.ads b/src/alire-conditional_values.ads
index 35446d45..f778e05f 100644
--- a/src/alire-conditional_values.ads
+++ b/src/alire-conditional_values.ads
@@ -1,5 +1,6 @@
 with Alire.Properties;
 with Alire.Requisites;
+with Alire.Utils;
 
 private with Ada.Containers.Indefinite_Holders;
 private with Ada.Containers.Indefinite_Vectors;
@@ -7,6 +8,7 @@ private with Ada.Containers.Indefinite_Vectors;
 generic
    type Values is private;
    with function "&" (L, R : Values) return Values;
+   with function Image (V : Values) return String;
 package Alire.Conditional_Values with Preelaborate is
 
    type Kinds is (Condition, Value, Vector);
@@ -34,6 +36,8 @@ package Alire.Conditional_Values with Preelaborate is
    function All_Values (This : Conditional_Value) return Values;
    --  Returns all values herein, both true and false, at any depth
 
+   function Image_One_Line (This : Conditional_Value) return String;
+
    ---------------
    --  SINGLES  --
    ---------------
@@ -71,6 +75,10 @@ private
 
    type Inner_Node is abstract tagged null record;
 
+   function Image (Node : Inner_Node) return String is abstract;
+
+   function Image_Classwide (Node : Inner_Node'Class) return String is (Node.Image);
+
    function Kind (This : Inner_Node'Class) return Kinds;
 
    package Holders is new Ada.Containers.Indefinite_Holders (Inner_Node'Class);
@@ -83,16 +91,36 @@ private
       Value : Values;
    end record;
 
+   overriding function Image (V : Value_Inner) return String is
+      (Image (V.Value));
+
    type Vector_Inner is new Inner_Node with record
       Values : Vectors.Vector;
    end record;
 
+   package Non_Primitive is
+      function One_Liner is new Utils.Image_One_Line
+        (Vectors,
+         Vectors.Vector,
+         Image_Classwide,
+         " and ",
+         "(empty condition)");
+   end Non_Primitive;
+
+   overriding function Image (V : Vector_Inner) return String is
+     (Non_Primitive.One_Liner (V.Values));
+
    type Conditional_Inner is new Inner_Node with record
       Condition  : Requisites.Tree;
       Then_Value : Conditional_Value;
       Else_Value : Conditional_Value;
    end record;
 
+   overriding function Image (V : Conditional_Inner) return String is
+     ("when " & V.Condition.Image &
+        " then " & V.Then_Value.Image_One_Line &
+        " else " & V.Else_Value.Image_One_Line);
+
    --------------
    -- As_Value --
    --------------
@@ -189,8 +217,11 @@ private
             else Condition));
 
    function Kind (This : Conditional_Value) return Kinds is
-      (This.Constant_Reference.Kind);
+     (This.Constant_Reference.Kind);
 
-   --  The price of doing this without pointers is this manual dispatching...
+   function Image_One_Line (This : Conditional_Value) return String is
+     (if This.Is_Empty
+      then "(empty condition)"
+      else This.Constant_Reference.Image);
 
 end Alire.Conditional_Values;
diff --git a/src/alire-dependencies-vectors.ads b/src/alire-dependencies-vectors.ads
index de63f8dd..41576db8 100644
--- a/src/alire-dependencies-vectors.ads
+++ b/src/alire-dependencies-vectors.ads
@@ -1,5 +1,7 @@
 with Ada.Containers.Indefinite_Vectors;
 
+with Alire.Utils;
+
 package Alire.Dependencies.Vectors with Preelaborate is
 
    --  Dependencies are a plain list (vector) of individual dependencies
@@ -9,6 +11,8 @@ package Alire.Dependencies.Vectors with Preelaborate is
 
    type Vector is new Dependency_Vectors.Vector with private;
 
+   function Image_One_Line (V : Vector) return String;
+
    function No_Dependencies return Vector;
 
    --  Creation of dependency vectors
@@ -33,4 +37,21 @@ private
                             Versions : Semantic_Versioning.Version_Set) return Vector is
      (To_Vector ((Name'Length, Name, To_Holder (Versions)), 1));
 
+   --------------------
+   -- Image_One_Line --
+   --------------------
+
+   package Non_Primitives is
+      function Image_One_Line_Instance is
+        new Utils.Image_One_Line (Dependency_Vectors,
+                                  Vector,
+                                  Image,
+                                  " and ",
+                                  "(no dependencies");
+   end Non_Primitives;
+
+   function Image_One_Line (V : Vector) return String renames Non_Primitives.Image_One_Line_Instance;
+
+--       (if V.Is_Empty then "(no dependencies)" else Image_With_Pos (V, 1));
+
 end Alire.Dependencies.Vectors;
diff --git a/src/alire-index.ads b/src/alire-index.ads
index 6380495e..2001a749 100644
--- a/src/alire-index.ads
+++ b/src/alire-index.ads
@@ -15,6 +15,7 @@ with Alire.Properties.Licenses;
 with Alire.Properties.Scenarios;
 with Alire.Releases;
 with Alire.Requisites;
+with Alire.Requisites.Dependencies;
 with Alire.Requisites.Platform;
 with Alire.Root_Project;
 
@@ -72,11 +73,13 @@ package Alire.Index is
    
    function Packaged_As (S : String) return Origins.Package_Names renames Origins.Packaged_As;
    
-   Unavailable : constant Origins.Package_Names := Origins.Unavailable;
+   function Unavailable return Origins.Package_Names renames Origins.Unavailable;
    
    function Native (Distros : Origins.Native_Packages) return Origins.Origin renames Origins.New_Native;
 
-   -- Shortcuts to give dependencies:
+   ------------------
+   -- Dependencies --
+   ------------------
 
    package Semver renames Semantic_Versioning;
 
@@ -94,11 +97,13 @@ package Alire.Index is
    --    Simpler if there's no exact release matching the versions we want to say
    --    Also needed for the generated _alr files which don't know about package names
 
+   function Unavailable return Release_Dependencies renames Releases.Unavailable;
+   --  A never available release
+   
    function Current (R : Release) return Release_Dependencies is
-     (On (R.Project, Semver.Within_Major (Semver.New_Version (Semver.Major (R.Version)))));
+     (On (R.Project, Semver.Within_Major (R.Version)));
    --  Within the major of R,
    --    it will accept the newest/oldest version according to the resolution policy (by default, newest)
-   --  Note: it might be older than R itself
 
    --  These take a release and use its name and version to derive a dependency
    function Within_Major is new Releases.From_Release (Semver.Within_Major);
@@ -125,13 +130,27 @@ package Alire.Index is
    function Exactly      is new Releases.From_Names (Semver.Exactly);
    function Except       is new Releases.From_Names (Semver.Except);   
    
+   function On_Condition (Condition  : Requisites.Tree;
+                          When_True  : Release_Dependencies;
+                          When_False : Release_Dependencies := No_Dependencies) 
+                          return       Release_Dependencies 
+                          renames      Conditional.For_Dependencies.New_Conditional;
+   --  Excplicitly conditional
+   
+   function When_Available (Preferred : Release_Dependencies;
+                            Otherwise : Release_Dependencies := Releases.Unavailable) 
+                            return Release_Dependencies is
+     (On_Condition (Requisites.Dependencies.New_Requisite (Preferred),
+                    Preferred,
+                    Otherwise));
+   --  Chained conditional dependencies (use first available)   
+   
    function "and" (L, R : Release_Dependencies) return Release_Dependencies 
                    renames Conditional.For_Dependencies."and";
 
    ------------------
-   --  PROPERTIES  --
+   --  Properties  --
    ------------------
-   -- (as vectors of conditionals) --
 
    use all type Alire.Dependencies.Vectors.Vector;
    use all type GPR.Value;
@@ -144,18 +163,13 @@ package Alire.Index is
    use all type Properties.Property'Class;
    use all type Release_Dependencies;
    use all type Release_Properties;
-   use all type Requisites.Tree;
-
-   --  Function for introducing conditional properties depending on platform conditions
-   function If_Platform (Condition  : Requisites.Tree;
-                         When_True  : Release_Dependencies;
-                         When_False : Release_Dependencies := No_Dependencies) 
-                         return       Release_Dependencies renames Conditional.For_Dependencies.New_Conditional;
+   use all type Requisites.Tree;   
    
-   function If_Platform (Condition  : Requisites.Tree;
-                         When_True  : Release_Properties;
-                         When_False : Release_Properties := No_Properties) 
-                         return       Release_Properties renames Conditional.For_Properties.New_Conditional;
+   function On_Condition (Condition  : Requisites.Tree;
+                          When_True  : Release_Properties;
+                          When_False : Release_Properties := No_Properties) 
+                          return       Release_Properties renames Conditional.For_Properties.New_Conditional;
+   --  Conditional properties
 
    --  Attributes (named pairs of label-value)
    --  We need them as Properties.Vector (inside conditionals) but also as
diff --git a/src/alire-properties-dependencies.ads b/src/alire-properties-dependencies.ads
new file mode 100644
index 00000000..d845d34e
--- /dev/null
+++ b/src/alire-properties-dependencies.ads
@@ -0,0 +1,44 @@
+with Alire.Dependencies.Vectors;
+with Alire.Properties;
+
+package Alire.Properties.Dependencies with Preelaborate is
+
+   type Availability_Checker is new Property with private;
+
+   type Checker_Function is access function (Dependencies : Alire.Dependencies.Vectors.Vector)
+                                             return Boolean;
+   --  The platform-bound function that says if a dependency is available
+   --  Currently, Alr.Query.Is_Resolvable
+
+   function New_Property (Checker : Checker_Function;
+                          Props   : Properties.Vector) return Vector;
+
+   function Checker (This : Availability_Checker) return Checker_Function;
+
+   function Properties (This : Availability_Checker) return Properties.Vector;
+   --  Contained platform properties
+
+private
+
+   type Availability_Checker is new Property with record
+      Checker    : Checker_Function;   -- Needed to check resolution
+      Properties : Alire.Properties.Vector;  -- Needed to materialize the conditional dependencies
+   end record;
+
+   overriding function Image (This : Availability_Checker) return String is
+     ("internal availability checker - OMG WHY ARE YOU SEEING THIS"); -- Don't think it should ever seen
+
+   function New_Property (Checker : Checker_Function;
+                          Props   : Alire.Properties.Vector) return Vector is
+     (+Availability_Checker'(Checker    => Checker,
+                             Properties => Props));
+
+   function Checker (This : Availability_Checker) return Checker_Function is
+     (This.Checker);
+
+   function Properties (This : Availability_Checker) return Alire.Properties.Vector is
+      (This.Properties);
+
+   -- FIXME currently there is no recursivity detection so mutually dependent packages will enter infinite loop
+
+end Alire.Properties.Dependencies;
diff --git a/src/alire-properties.ads b/src/alire-properties.ads
index dc792e38..503cdb04 100644
--- a/src/alire-properties.ads
+++ b/src/alire-properties.ads
@@ -1,5 +1,7 @@
 with Ada.Containers.Indefinite_Vectors;
 
+with Alire.Utils;
+
 package Alire.Properties with Preelaborate is
 
    --  Properties are the general mechanism used to store all info about a release.
@@ -31,6 +33,8 @@ package Alire.Properties with Preelaborate is
    function "and" (L, R : Vector) return Vector;
    function "+" (P : Property'Class) return Vector;
 
+   function Image_One_Line (V : Vector) return String;
+
    --  A generic helper to simply store/retrieve e.g. an enumerated type
    generic
       type Value is private;
@@ -75,4 +79,15 @@ private
 --     function "and" (L, R : Property'Class) return Vector is (L & R);
 --     function "and" (L : Vector; R : Property'Class) return Vector is (L & R);
 
+   package Non_Primitives is
+      function Image_One_Line_Instance is
+        new Utils.Image_One_Line (Vectors,
+                                  Vector,
+                                  Image_Classwide,
+                                  " and ",
+                                  "(no properties");
+   end Non_Primitives;
+
+   function Image_One_Line (V : Vector) return String renames Non_Primitives.Image_One_Line_Instance;
+
 end Alire.Properties;
diff --git a/src/alire-releases.ads b/src/alire-releases.ads
index 40186e6e..175d3595 100644
--- a/src/alire-releases.ads
+++ b/src/alire-releases.ads
@@ -75,6 +75,7 @@ package Alire.Releases with Preelaborate is
    --  True if some property contains the given string
    
    --  Dependency generation helpers for all semantic versioning functions:
+   --  These are here to avoid a 'body not seen' Program_Error if they were in Index
    
    function On (Name     : Project_Name; 
                 Versions : Semantic_Versioning.Version_Set)
@@ -89,7 +90,13 @@ package Alire.Releases with Preelaborate is
    function From_Names (P : Project_Name; 
                         V : Semantic_Versioning.Version) return Conditional.Dependencies;   
 
+   function Unavailable return Conditional.Dependencies;
+   --  A never available dependency that is useful in conditional chained dependencies (see Index)
+   
 private
+   
+   function Unavailable return Conditional.Dependencies is 
+     (On ("alire_unavailable", Semantic_Versioning.Any));
 
    use Properties;
    function Describe is new Properties.Labeled.Cond_New_Label (Properties.Labeled.Description);
@@ -138,8 +145,7 @@ private
    
    function Depends (R : Release;
                      P : Properties.Vector)
-                     return Dependencies.Vector is
-     (R.Dependencies.Evaluate (P));
+                     return Dependencies.Vector is (R.Dependencies.Evaluate (P));
    
    function Origin  (R : Release) return Origins.Origin is (R.Origin);
    function Available (R : Release) return Requisites.Tree is (R.Available);
diff --git a/src/alire-requisites-dependencies.ads b/src/alire-requisites-dependencies.ads
new file mode 100644
index 00000000..77584e9e
--- /dev/null
+++ b/src/alire-requisites-dependencies.ads
@@ -0,0 +1,39 @@
+with Alire.Conditional;
+with Alire.Properties.Dependencies;
+
+package Alire.Requisites.Dependencies with Preelaborate is
+
+   --  Special requisite that is fulfilled when a dependency is available on a platform
+   --  This is checked against a special property that encapsulates the check of
+   --    actual packages available once the platform is known
+
+   package Typed is new Typed_Requisites (Properties.Dependencies.Availability_Checker);
+
+   type Requisite is new Typed.Requisite with private;
+
+   function New_Requisite (On : Conditional.Dependencies) return Tree;
+
+   overriding function Is_Satisfied (R : Requisite;
+                                     P : Properties.Dependencies.Availability_Checker)
+                                     return Boolean;
+
+   overriding function Image (R : Requisite) return String;
+
+private
+
+   type Requisite is new Typed.Requisite with record
+      Deps : Conditional.Dependencies;
+   end record;
+
+   function New_Requisite (On : Conditional.Dependencies) return Tree is
+      (Trees.Leaf (Requisite'(Deps => On)));
+
+   overriding function Is_Satisfied (R : Requisite;
+                                     P : Properties.Dependencies.Availability_Checker)
+                                     return Boolean is
+     (P.Checker.all (R.Deps.Evaluate (P.Properties)));
+
+   overriding function Image (R : Requisite) return String is
+      (R.Deps.Image_One_Line & " resolvable");
+
+end Alire.Requisites.Dependencies;
diff --git a/src/alire-requisites.ads b/src/alire-requisites.ads
index 05294ebf..7fe71854 100644
--- a/src/alire-requisites.ads
+++ b/src/alire-requisites.ads
@@ -70,8 +70,6 @@ package Alire.Requisites with Preelaborate is
          then Requisite'Class (R).Is_Satisfied (Compatible_Property (P))
          else False);
 
-      --  For free we get a requisite that is equality for value properties
-
    end Typed_Requisites;
 
    --------------
diff --git a/src/alire-types.ads b/src/alire-types.ads
index 7f647330..a739aa06 100644
--- a/src/alire-types.ads
+++ b/src/alire-types.ads
@@ -1,12 +1,16 @@
 with Alire.Conditional;
+with Alire.Dependencies;
 with Alire.Dependencies.Vectors;
 
 package Alire.Types with Preelaborate is
 
    --  Recopilation of types for convenient use and documentation
 
+   subtype Dependency is Dependencies.Dependency;
+   -- A single dependency on a single project+versions
+
    subtype Platform_Dependencies is Dependencies.Vectors.Vector;
-   -- A plain vector
+   -- A plain vector, all dependencies must be met
 
    subtype Abstract_Dependencies is Conditional.Dependencies;
    -- Conditional dependencies as yet unmaterialized for a precise platform
diff --git a/src/alire-utils.adb b/src/alire-utils.adb
index 7bc4ca10..135bdad8 100644
--- a/src/alire-utils.adb
+++ b/src/alire-utils.adb
@@ -78,4 +78,26 @@ package body Alire.Utils is
       end return;
    end To_Mixed_Case;
 
+   --------------------
+   -- Image_One_Line --
+   --------------------
+
+   function Image_One_Line (V : Vector) return String is
+
+      use all type Vectors.Index_Type;
+
+      function Image (V : Vector; Pos : Vectors.Index_Type) return String is
+        (Image (V.Element (Pos)) &
+         (if Pos = V.Last_Index
+          then ""
+          else Separator & Image (V, Pos + 1)));
+
+   begin
+      if V.Is_Empty then
+         return When_Empty;
+      else
+         return Image (V, V.First_Index);
+      end if;
+   end Image_One_Line;
+
 end Alire.Utils;
diff --git a/src/alire-utils.ads b/src/alire-utils.ads
index 98063792..7a9c2e79 100644
--- a/src/alire-utils.ads
+++ b/src/alire-utils.ads
@@ -15,6 +15,14 @@ package Alire.Utils with Preelaborate is
    --  If Str contains Separator, the rhs is returned
    --  Otherwise ""
 
+   generic
+      with package Vectors is new Ada.Containers.Indefinite_Vectors (<>);
+      type Vector is new Vectors.Vector with private;
+      with function Image (Item : Vectors.Element_Type) return String is <>;
+      Separator  : String := " ";
+      When_Empty : String := "(empty)";
+   function Image_One_Line (V : Vector) return String;
+
    --------------------
    -- String_Vectors --
    --------------------