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
-      } ;
-
 }