diff --git a/lib/ast.ml b/lib/ast.ml
index 5b3b884..4a000be 100644
--- a/lib/ast.ml
+++ b/lib/ast.ml
@@ -16,14 +16,16 @@ and join_type =
   | Union
   | Natural
 and condition = 
-  | Condition of string * predicate
+  | Condition of predicand * predicate
   | And of condition * condition
   | Or of condition * condition
   | Not of condition
+and predicand = 
+  | Ref of string
 and predicate = 
-  | Comparison of operator * string
-  | Between of string * string
-  | NotBetween of string * string
+  | Comparison of operator * predicand
+  | Between of predicand * predicand
+  | NotBetween of predicand * predicand
   | In of string list
   | NotIn of string list
   | Like of string
diff --git a/parser/parser.mly b/parser/parser.mly
index a16468e..e79cef8 100644
--- a/parser/parser.mly
+++ b/parser/parser.mly
@@ -110,7 +110,8 @@ parenthesized_value_expression:
   | LEFT_PAREN value_expression RIGHT_PAREN { $2 }
 
 nonparenthesized_value_expression_primary:
-  | column_reference { $1 }
+  | column_reference { Ref($1) }
+  (*| set_function_specification { Ref("function") } *)
 
 (***************************)
 
@@ -443,8 +444,8 @@ as_clause :
 
 predicate :
   | comparison_predicate { $1 }
-  | between_predicate { $1 } 
-  | in_predicate { $1 }
+(*  | between_predicate { $1 } *)
+(*  | in_predicate { $1 } *)
 (*  | like_predicate { $1 }*)
 
 (*****************)
@@ -536,14 +537,14 @@ search_condition:
 (* 10.9 AGGREGATE FUNCTION *)
 
 aggregate_function:
-  | COUNT LEFT_PAREN ASTERISK RIGHT_PAREN { Asterisk }
-  | COUNT LEFT_PAREN ASTERISK RIGHT_PAREN filter_clause { Asterisk }
-  | general_set_function { $1 }
-  | general_set_function filter_clause { $1 }
+  | COUNT LEFT_PAREN ASTERISK RIGHT_PAREN { }
+  | COUNT LEFT_PAREN ASTERISK RIGHT_PAREN filter_clause { }
+  | general_set_function { }
+  | general_set_function filter_clause { }
 
 general_set_function:
-  | set_function_type LEFT_PAREN value_expression RIGHT_PAREN { $3 }
-  | set_function_type LEFT_PAREN set_quantifier value_expression RIGHT_PAREN { $4 }
+  | set_function_type LEFT_PAREN value_expression RIGHT_PAREN { }
+  | set_function_type LEFT_PAREN set_quantifier value_expression RIGHT_PAREN { }
 
 set_function_type:
   | computationnal_operation {}
diff --git a/test/test_ast.ml b/test/test_ast.ml
index 4e366f4..21ffc2e 100644
--- a/test/test_ast.ml
+++ b/test/test_ast.ml
@@ -30,8 +30,8 @@ let test_default_join () =
         Table("t2"),
         Some(
           Condition(
-            "a",
-            Comparison(Equals, "b")
+            Ref("a"),
+            Comparison(Equals, Ref("b"))
           )
         )
       )],
@@ -50,8 +50,8 @@ let test_left_join () =
         Table("t2"),
         Some(
           Condition(
-            "a",
-            Comparison(Equals, "b")
+            Ref("a"),
+            Comparison(Equals, Ref("b"))
           )
         )
       )],
@@ -70,8 +70,8 @@ let test_right_join () =
         Table("t2"),
         Some(
           Condition(
-            "a",
-            Comparison(Equals, "b")
+            Ref("a"),
+            Comparison(Equals, Ref("b"))
           )
         )
       )],
@@ -90,8 +90,8 @@ let test_inner_join () =
         Table("t2"),
         Some(
           Condition(
-            "a",
-            Comparison(Equals, "b")
+            Ref("a"),
+            Comparison(Equals, Ref("b"))
           )
         )
       )],
@@ -156,8 +156,8 @@ let test_join_join () =
           Table("t2"),
           Some(
             Condition(
-              "a",
-              Comparison(Equals, "b")
+              Ref("a"),
+              Comparison(Equals, Ref("b"))
             )
           ) 
         ),
@@ -165,8 +165,8 @@ let test_join_join () =
         Table("t3"),
         Some(
           Condition(
-            "a",
-            Comparison(Equals, "c")
+            Ref("a"),
+            Comparison(Equals, Ref("c"))
           )
         )
       )