Index: src/natools-smaz-tools.adb
==================================================================
--- src/natools-smaz-tools.adb
+++ src/natools-smaz-tools.adb
@@ -841,6 +841,29 @@
         (Size => Word'Length,
          Word => Word,
          Score => Score_Value (Word_Maps.Element (Cursor)) * Word'Length);
    end To_Scored_Word;
 
+
+   function Worst_Index
+     (Dict : in Dictionary;
+      Counts : in Dictionary_Counts;
+      Method : in Methods.Enum)
+     return Ada.Streams.Stream_Element
+   is
+      Result : Ada.Streams.Stream_Element := 0;
+      Worst_Score : Score_Value := Score_Encoded (Dict, Counts, 0);
+      S : Score_Value;
+   begin
+      for I in 1 .. Dict.Dict_Last loop
+         S := Score (Dict, Counts, I, Method);
+
+         if S < Worst_Score then
+            Result := I;
+            Worst_Score := S;
+         end if;
+      end loop;
+
+      return Result;
+   end Worst_Index;
+
 end Natools.Smaz.Tools;

Index: src/natools-smaz-tools.ads
==================================================================
--- src/natools-smaz-tools.ads
+++ src/natools-smaz-tools.ads
@@ -118,10 +118,15 @@
       --  used with Dictionary.Hash.
 
    type String_Count is range 0 .. 2 ** 31 - 1;
       --  Type for a number of substring occurrences
 
+   package Methods is
+      type Enum is (Encoded, Frequency, Gain);
+   end Methods;
+      --  Evaluation methods to select words to remove or include
+
    type Word_Counter is private;
       --  Accumulate frequency/occurrence counts for a set of strings
 
    procedure Add_Word
      (Counter : in out Word_Counter;
@@ -184,10 +189,63 @@
       Counts : in out Dictionary_Counts);
       --  Compress all strings of Corpus, returning the total number of
       --  compressed bytes and the number of uses for each dictionary
       --  element.
 
+   function Worst_Index
+     (Dict : in Dictionary;
+      Counts : in Dictionary_Counts;
+      Method : in Methods.Enum)
+     return Ada.Streams.Stream_Element;
+      --  Return the element with worst score
+
+
+   type Score_Value is range 0 .. 2 ** 31 - 1;
+
+   function Length
+     (Dict : in Dictionary;
+      E : in Ada.Streams.Stream_Element)
+     return Score_Value
+     is (Natools.Smaz.Dict_Entry (Dict, E)'Length);
+      --  Length of a dictionary entry
+
+   function Score_Encoded
+     (Dict : in Dictionary;
+      Counts : in Natools.Smaz.Tools.Dictionary_Counts;
+      E : Ada.Streams.Stream_Element)
+     return Score_Value
+     is (Score_Value (Counts (E)) * Length (Dict, E));
+      --  Score value using the amount of encoded data using E
+
+   function Score_Frequency
+     (Dict : in Dictionary;
+      Counts : in Natools.Smaz.Tools.Dictionary_Counts;
+      E : Ada.Streams.Stream_Element)
+     return Score_Value
+     is (Score_Value (Counts (E)));
+      --  Score value using the number of times E was used
+
+   function Score_Gain
+     (Dict : in Dictionary;
+      Counts : in Natools.Smaz.Tools.Dictionary_Counts;
+      E : Ada.Streams.Stream_Element)
+     return Score_Value
+     is (Score_Value (Counts (E)) * (Length (Dict, E) - 1));
+      --  Score value using the number of bytes saved using E
+
+   function Score
+     (Dict : in Dictionary;
+      Counts : in Natools.Smaz.Tools.Dictionary_Counts;
+      E : in Ada.Streams.Stream_Element;
+      Method : in Methods.Enum)
+     return Score_Value
+     is (case Method is
+         when Methods.Encoded => Score_Encoded (Dict, Counts, E),
+         when Methods.Frequency => Score_Frequency (Dict, Counts, E),
+         when Methods.Gain => Score_Gain (Dict, Counts, E));
+      --  Scare value with dynamically chosen method
+
 private
 
    package Word_Maps is new Ada.Containers.Indefinite_Ordered_Maps
      (String, String_Count);
 
@@ -194,12 +252,10 @@
    type Word_Counter is record
       Map : Word_Maps.Map;
    end record;
 
 
-   type Score_Value is range 0 .. 2 ** 31 - 1;
-
    type Scored_Word (Size : Natural) is record
       Word : String (1 .. Size);
       Score : Score_Value;
    end record;