src/HOL/Tools/Nitpick/nitpick_nut.ML

           let val R1 = Atom (spec_of_type scope (domain_type T)) in
             Cst (NormFrac, T, Func (R1, Func (R1, Opt (Struct [R1, R1]))))
           end
         | Cst (cst, T, _) =>
           if cst = Unknown orelse cst = Unrep then
-            case (is_boolean_type T, polar) of
+            case (is_boolean_type T, polar |> unsound ? flip_polarity) of
               (true, Pos) => Cst (False, T, Formula Pos)
             | (true, Neg) => Cst (True, T, Formula Neg)
             | _ => Cst (cst, T, best_opt_set_rep_for_type scope T)
           else if member (op =) [Add, Subtract, Multiply, Divide, Gcd, Lcm]
                          cst then