diff --git a/examples/tutorial/calculator/CalculatorC.gf b/examples/tutorial/calculator/CalculatorC.gf
index cfef0e717..e36c28e3f 100644
--- a/examples/tutorial/calculator/CalculatorC.gf
+++ b/examples/tutorial/calculator/CalculatorC.gf
@@ -1,6 +1,6 @@
 --# -path=.:prelude
 
-concrete CalculatorC of Calculator = open Predef,Prelude in {
+concrete CalculatorC of Calculator = open Prelude, Formal in {
 
   flags lexer=codevars ; unlexer=code ;
 
@@ -21,39 +21,4 @@ concrete CalculatorC of Calculator = open Predef,Prelude in {
     EInt i = constant i.s ;
     EVar x = constant x.s ;
 
-  oper
-    Prec : PType = Ints 2 ;
-    TermPrec : Type = {s : Str ; p : Prec} ;
-
-    lessPrec : Prec -> Prec -> Bool = \p,q ->
-      case <<p,q> : Prec * Prec> of {
-        <1,1> | <1,0> | <0,0> => False ;
-        <1,_> | <0,_>         => True ;
-        _ => False
-        } ;
-
-    usePrec : TermPrec -> Prec -> Str = \x,p ->
-      case lessPrec x.p p of {
-        True => paren x.s ;
-        False => noparen x.s
-      } ;
-
-    paren : Str -> Str = \s -> "(" ++ s ++ ")" ;
-    noparen : Str -> Str = \s -> variants {s ; "(" ++ s ++ ")"} ;
-
-    top : TermPrec -> Str = \t -> usePrec t 0 ;
-
-    mkPrec : Prec -> Str -> TermPrec = \p,s -> 
-      {s = s ; p = p} ;
-
-    constant : Str -> TermPrec = mkPrec 2 ;
-
-    infixl : Prec -> Str -> (_,_ : TermPrec) -> TermPrec = \p,f,x,y ->
-      mkPrec p (usePrec x p ++ f ++ usePrec y (nextPrec p)) ;
-
-    nextPrec : Prec -> Prec = \p -> case <p : Prec> of {
-      2 => 2 ; 
-      n => plus n 1
-      } ;
-
 }
diff --git a/lib/prelude/Formal.gf b/lib/prelude/Formal.gf
new file mode 100644
index 000000000..2aa33d9ef
--- /dev/null
+++ b/lib/prelude/Formal.gf
@@ -0,0 +1,54 @@
+resource Formal = open Prelude in {
+
+-- to replace the old library Precedence
+
+  oper
+    Prec : PType ;
+    TermPrec : Type = {s : Str ; p : Prec} ;
+
+    mkPrec : Prec -> Str -> TermPrec = \p,s -> 
+      {s = s ; p = p} ;
+
+    top : TermPrec -> Str = usePrec 0 ;
+
+    constant : Str -> TermPrec = mkPrec highest ;
+
+    infixl : Prec -> Str -> (_,_ : TermPrec) -> TermPrec = \p,f,x,y ->
+      mkPrec p (usePrec p x ++ f ++ usePrec (nextPrec p) y) ;
+    infixr : Prec -> Str -> (_,_ : TermPrec) -> TermPrec = \p,f,x,y ->
+      mkPrec p (usePrec (nextPrec p) x ++ f ++ usePrec p y) ;
+    infixn : Prec -> Str -> (_,_ : TermPrec) -> TermPrec = \p,f,x,y ->
+      mkPrec p (usePrec (nextPrec p) x ++ f ++ usePrec (nextPrec p) y) ;
+
+-- auxiliaries, should not be needed so much
+
+    usePrec : Prec -> TermPrec -> Str = \p,x ->
+      case lessPrec x.p p of {
+        True => parenth x.s ;
+        False => parenthOpt x.s
+      } ;
+
+    parenth : Str -> Str = \s -> "(" ++ s ++ ")" ;
+    parenthOpt : Str -> Str = \s -> variants {s ; "(" ++ s ++ ")"} ;
+
+--.
+-- low-level things: don't use
+
+    Prec : PType = Predef.Ints 4 ;
+
+    highest = 4 ;
+
+    lessPrec : Prec -> Prec -> Bool = \p,q ->
+      case <<p,q> : Prec * Prec> of {
+        <3,4> | <2,3> | <2,4> => True ;
+        <1,1> | <1,0> | <0,0> => False ;
+        <1,_> | <0,_>         => True ;
+        _ => False
+        } ;
+
+    nextPrec : Prec -> Prec = \p -> case <p : Prec> of {
+      4 => 4 ; 
+      n => Predef.plus n 1
+      } ;
+
+}