diff --git a/include/sqlpp11/core/operator/arithmetic_expression.h b/include/sqlpp11/core/operator/arithmetic_expression.h
index 960560fc..5d2f7ea1 100644
--- a/include/sqlpp11/core/operator/arithmetic_expression.h
+++ b/include/sqlpp11/core/operator/arithmetic_expression.h
@@ -88,45 +88,15 @@ namespace sqlpp
     using type = detail::type_vector<L, R>;
   };
 
-#if 0
-
   template <typename L, typename Operator, typename R>
-  struct value_type_of_t<arithmetic_expression<L, Operator, R>>
-  {
-    using type = numeric_t;
-  };
+  struct requires_braces<arithmetic_expression<L, Operator, R>> : public std::true_type{};
 
-  template <typename L, typename Operator, typename R>
-  constexpr auto requires_braces_v<arithmetic_expression<L, Operator, R>> = true;
-
-  template <typename Context, typename L, typename Operator, typename R>
-  [[nodiscard]] auto to_sql_string(Context& context, const arithmetic_expression<L, Operator, R>& t)
-  {
-    return to_sql_string(context, embrace(t._l)) + Operator::symbol + to_sql_string(context, embrace(t._r));
-  }
-
-  template <typename Context, typename Operator, typename R>
-  [[nodiscard]] auto to_sql_string(Context& context, const arithmetic_expression<none_t, Operator, R>& t)
-  {
-    return Operator::symbol + to_sql_string(context, embrace(t._r));
-  }
-
-  template <typename Context, typename L1, typename Operator, typename R1, typename R2>
-  [[nodiscard]] auto to_sql_string(Context& context,
-                                   const arithmetic_expression<arithmetic_expression<L1, Operator, R1>, Operator, R2>& t)
-  {
-    return to_sql_string(context, t._l) + Operator::symbol + to_sql_string(context, embrace(t._r));
-  }
-#endif
-  
   template <typename Context, typename L, typename Operator, typename R>
   auto serialize(Context& context, const arithmetic_expression<L, Operator, R>& t) -> Context&
   {
-    context << "(";
     serialize_operand(context, t._l);
     context << Operator::symbol;
     serialize_operand(context, t._r);
-    context << ")";
     return context;
   }
 
diff --git a/include/sqlpp11/core/operator/as_expression.h b/include/sqlpp11/core/operator/as_expression.h
index 3509e890..87afeccc 100644
--- a/include/sqlpp11/core/operator/as_expression.h
+++ b/include/sqlpp11/core/operator/as_expression.h
@@ -39,11 +39,6 @@ namespace sqlpp
     using _traits = make_traits<value_type_of_t<Expression>, tag::is_selectable, tag::is_alias>;
 
 #warning Maybe make constructor of expressions private to force construction in the respective functions?
-    /*
-    static_assert(is_expression_t<Expression>::value, "invalid argument for an expression alias");
-    static_assert(not is_alias_t<Expression>::value, "cannot create an alias of an alias");
-    */
-
     constexpr as_expression(Expression expression) : _expression(std::move(expression))
     {
     }
diff --git a/include/sqlpp11/core/operator/assign_expression.h b/include/sqlpp11/core/operator/assign_expression.h
index fe7bad43..e85b275c 100644
--- a/include/sqlpp11/core/operator/assign_expression.h
+++ b/include/sqlpp11/core/operator/assign_expression.h
@@ -77,22 +77,7 @@ namespace sqlpp
     using type = R;
   };
 
-  /*
-  template <typename L, typename R>
-  struct column_of<assign_t<L, R>>
-  {
-    using type = L;
-  };
-
-  template <typename L, typename R>
-  constexpr auto requires_braces_v<assign_t<L, R>> = true;
-
-  template <typename Context, typename L, typename R>
-  [[nodiscard]] auto to_sql_string(Context& context, const assign_t<L, R>& t)
-  {
-    return to_sql_string(context, t.column) + " = " + to_sql_string(context, embrace(t.value));
-  }
-  */
+#warning does this require braces?
 
   template <typename Context, typename L, typename Operator, typename R>
   Context& serialize(Context& context, const assign_expression<L, Operator, R>& t)
diff --git a/include/sqlpp11/core/operator/between_expression.h b/include/sqlpp11/core/operator/between_expression.h
index df47b938..e0b47d42 100644
--- a/include/sqlpp11/core/operator/between_expression.h
+++ b/include/sqlpp11/core/operator/between_expression.h
@@ -67,38 +67,8 @@ namespace sqlpp
     using type = detail::type_vector<L, R1, R2>;
   };
 
-
-  /*
-
-  template <typename L, typename... Args>
-  struct nodes_of<between_t<L, Args...>>
-  {
-    using type = type_vector<L, Args...>;
-  };
-
-  template <typename L, typename... Args>
-  constexpr auto in(L l, Args... args)
-      -> ::sqlpp::enable_if_t<((sizeof...(Args) > 0) and ... and values_are_compatible_v<L, Args>), between_t<L, Args...>>
-  {
-    return between_t<L, Args...>{l, std::tuple{args...}};
-  }
-
-  template <typename L, typename... Args>
-  constexpr auto requires_braces_v<between_t<L, Args...>> = true;
-
-  template <typename Context, typename L, typename... Args>
-  [[nodiscard]] auto to_sql_string(Context& context, const between_t<L, Args...>& t)
-  {
-    if constexpr (sizeof...(Args) == 1)
-    {
-      return to_sql_string(context, embrace(t.l)) + " IN(" + to_sql_string(context, std::get<0>(t.args)) + ")";
-    }
-    else
-    {
-      return to_sql_string(context, embrace(t.l)) + " IN(" + tuple_to_sql_string(context, ", ", t.args) + ")";
-    }
-  }
-  */
+  template <typename L, typename R1, typename R2>
+  struct requires_braces<between_expression<L, R1, R2>> : public std::true_type{};
 
 #warning: Need tests for between expressions
   template <typename L, typename R1, typename R2, typename = check_between_args<L, R1, R2>>
@@ -107,52 +77,15 @@ namespace sqlpp
     return {std::move(l), std::move(r1), std::move(r2)};
   }
 
-#if 0 // original serialize implementation
-  template <typename Context, typename Operand, typename Arg, typename... Args>
-  Context& serialize(Context& context, const between_t<Operand, Arg, Args...>& t)
+  template <typename Context, typename L, typename R1, typename R2>
+  auto serialize(Context& context, const between_expression<L, R1, R2>& t) -> Context&
   {
-    serialize(context, t._operand);
-    context << " IN(";
-    if (sizeof...(Args) == 0)
-    {
-      serialize(context, std::get<0>(t._args));
-    }
-    else
-    {
-      interpret_tuple(t._args, ',', context);
-    }
-    context << ')';
+    serialize_operand(context, t._l);
+    context << " BETWEEN ";
+    serialize_operand(context, t._r1);
+    context << " AND ";
+    serialize_operand(context, t._r2);
     return context;
   }
 
-  template <typename Context, typename Operand>
-  Context& serialize(Context& context, const between_t<Operand>&)
-  {
-    serialize(context, boolean_operand{false});
-    return context;
-  }
-
-  template <typename Container>
-  struct value_list_t;
-
-  template <typename Context, typename Operand, typename Container>
-  Context& serialize(Context& context, const between_t<Operand, value_list_t<Container>>& t)
-  {
-    const auto& value_list = std::get<0>(t._args);
-    if (value_list._container.empty())
-    {
-      serialize(context, boolean_operand{false});
-    }
-    else
-    {
-      serialize(context, t._operand);
-      context << " IN(";
-      serialize(context, value_list);
-      context << ')';
-    }
-    return context;
-  }
-
-#endif
-
 }  // namespace sqlpp
diff --git a/include/sqlpp11/core/operator/bit_expression.h b/include/sqlpp11/core/operator/bit_expression.h
index 559af420..ef0fdcc9 100644
--- a/include/sqlpp11/core/operator/bit_expression.h
+++ b/include/sqlpp11/core/operator/bit_expression.h
@@ -71,37 +71,15 @@ namespace sqlpp
   template <typename L, typename R>
   using check_bit_shift_expression_args = ::sqlpp::enable_if_t<is_integral<L>::value and (is_integral<R>::value or is_unsigned_integral<R>::value)>;
 
-#if 0
   template <typename L, typename Operator, typename R>
-  struct value_type_of_t<binary_t<L, Operator, R>>
-  {
-    using type = integral_t;
-  };
-
-  template <typename L, typename Operator, typename R>
-  constexpr auto requires_braces_v<binary_t<L, Operator, R>> = true;
-
-  template <typename Context, typename L, typename Operator, typename R>
-  [[nodiscard]] auto to_sql_string(Context& context, const binary_t<L, Operator, R>& t)
-  {
-    return to_sql_string(context, embrace(t._l)) + Operator::symbol + to_sql_string(context, embrace(t._r));
-  }
-
-  template <typename Context, typename Operator, typename R>
-  [[nodiscard]] auto to_sql_string(Context& context, const binary_t<none_t, Operator, R>& t)
-  {
-    return Operator::symbol + to_sql_string(context, embrace(t._r));
-  }
-#endif
+  struct requires_braces<bit_expression<L, Operator, R>> : public std::true_type {};
 
   template <typename Context, typename L, typename Operator, typename R>
   auto serialize(Context& context, const bit_expression<L, Operator, R>& t) -> Context&
   {
-    context << "(";
     serialize_operand(context, t._l);
     context << Operator::symbol;
     serialize_operand(context, t._r);
-    context << ")";
     return context;
   }
 
diff --git a/include/sqlpp11/core/operator/case.h b/include/sqlpp11/core/operator/case.h
index 062c7b93..a6aa31c1 100644
--- a/include/sqlpp11/core/operator/case.h
+++ b/include/sqlpp11/core/operator/case.h
@@ -86,6 +86,9 @@ namespace sqlpp
   {
   };
 
+  template <typename When, typename Then, typename Else>
+  struct requires_braces<case_t<When, Then, Else>> : public std::true_type{};
+
   template <typename When, typename Then>
   class case_then_t
   {
@@ -156,13 +159,13 @@ namespace sqlpp
   template <typename Context, typename When, typename Then, typename Else>
   Context& serialize(Context& context, const case_t<When, Then, Else>& t)
   {
-    context << "(CASE WHEN ";
+    context << "CASE WHEN ";
     serialize(context, t._when);
     context << " THEN ";
     serialize(context, t._then);
     context << " ELSE ";
     serialize(context, t._else);
-    context << " END)";
+    context << " END";
     return context;
   }
 
diff --git a/include/sqlpp11/core/operator/comparison_expression.h b/include/sqlpp11/core/operator/comparison_expression.h
index 72e56250..8c5e22d3 100644
--- a/include/sqlpp11/core/operator/comparison_expression.h
+++ b/include/sqlpp11/core/operator/comparison_expression.h
@@ -84,48 +84,15 @@ namespace sqlpp
     using type = detail::type_vector<L, R>;
   };
 
-
-#if 0
-  SQLPP_WRAPPED_STATIC_ASSERT(assert_comparison_operands_are_compatible,
-                              "comparison operands must have compatible value types");
-
-  template <typename L, typename R>
-  constexpr auto check_comparison_args()
-  {
-    if constexpr (not values_are_compatible_v<L, R>)
-    {
-      return failed<assert_comparison_operands_are_compatible>{};
-    }
-    else
-    {
-      return succeeded{};
-    }
-  }
-
   template <typename L, typename Operator, typename R>
-  struct value_type_of_t<comparison_expression<L, Operator, R>>
-  {
-    using type = bool;
-  };
-
-  template <typename L, typename Operator, typename R>
-  constexpr auto requires_braces_v<comparison_expression<L, Operator, R>> = true;
-
-  template <typename Context, typename L, typename Operator, typename R>
-  [[nodiscard]] auto to_sql_string(Context& context, const comparison_expression<L, Operator, R>& t)
-  {
-    return to_sql_string(context, embrace(t.l)) + Operator::symbol + to_sql_string(context, embrace(t.r));
-  }
-#endif
+  struct requires_braces<comparison_expression<L, Operator, R>> : public std::true_type{};
 
   template <typename Context, typename L, typename Operator, typename R>
   auto serialize(Context& context, const comparison_expression<L, Operator, R>& t) -> Context&
   {
-    context << "(";
     serialize_operand(context, t._l);
     context << Operator::symbol;
     serialize_operand(context, t._r);
-    context << ")";
     return context;
   }
 
diff --git a/include/sqlpp11/core/operator/exists_expression.h b/include/sqlpp11/core/operator/exists_expression.h
index 001f4a71..f1fe7f87 100644
--- a/include/sqlpp11/core/operator/exists_expression.h
+++ b/include/sqlpp11/core/operator/exists_expression.h
@@ -66,7 +66,7 @@ namespace sqlpp
   template <typename Context, typename Select>
   auto serialize(Context& context, const exists_expression<Select>& t) -> Context&
   {
-    context << "EXISTS(";
+    context << "EXISTS (";
     serialize(context, t._select);
     context << ")";
     return context;
diff --git a/include/sqlpp11/core/operator/in_expression.h b/include/sqlpp11/core/operator/in_expression.h
index 968b2a78..5b7de06e 100644
--- a/include/sqlpp11/core/operator/in_expression.h
+++ b/include/sqlpp11/core/operator/in_expression.h
@@ -95,26 +95,22 @@ namespace sqlpp
     using type = detail::type_vector<L, R>;
   };
 
+  template <typename L, typename Operator, typename R>
+  struct requires_braces<in_expression<L, Operator, std::vector<R>>> : public std::true_type{};
+
   template <typename L, typename Operator, typename... Args>
   struct nodes_of<in_expression<L, Operator, std::tuple<Args...>>>
   {
     using type = detail::type_vector<L, Args...>;
   };
 
-  /*
-
-  template <typename L, typename Operator, typename R>
-  constexpr auto requires_braces_v<in_expression<L, operator, std::vector<R>>> = true;
-
-  template <typename L, typename... Args>
-  constexpr auto requires_braces_v<in_expression<L, std::tuple<Args...>>> = true;
-
-  */
+  template <typename L, typename Operator, typename... Args>
+  struct requires_braces<in_expression<L, Operator, std::tuple<Args...>>> : public std::true_type{};
 
   template <typename Context, typename L, typename Operator, typename... Args>
-  Context& serialize(Context& context, const in_expression<L, Operator, std::tuple<Args...>>& t)
+  auto serialize(Context& context, const in_expression<L, Operator, std::tuple<Args...>>& t) -> Context&
   {
-    serialize(context, t._l);
+    serialize_operand(context, t._l);
     context << Operator::symbol << "(";
     if (sizeof...(Args) == 1)
     {
@@ -122,7 +118,7 @@ namespace sqlpp
     }
     else
     {
-#warning: interpret_tuple arguments should be reverted, too
+#warning: interpret_tuple arguments should take Context first, too
       interpret_tuple(t._r, ',', context);
     }
     context << ')';
diff --git a/include/sqlpp11/core/operator/logical_expression.h b/include/sqlpp11/core/operator/logical_expression.h
index 1a6e3863..2b6c102e 100644
--- a/include/sqlpp11/core/operator/logical_expression.h
+++ b/include/sqlpp11/core/operator/logical_expression.h
@@ -31,8 +31,6 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include <sqlpp11/core/operator/enable_as.h>
 #include <sqlpp11/core/query/dynamic.h>
 #include <sqlpp11/core/noop.h>
-//#include <sqlpp11/embrace.h>
-//#include <sqlpp11/to_sql_string.h>
 #include <sqlpp11/core/type_traits.h>
 
 namespace sqlpp
@@ -71,45 +69,18 @@ namespace sqlpp
     using type = detail::type_vector<L, R>;
   };
 
-  /*
   template <typename L, typename Operator, typename R>
-  struct value_type_of_t<logical_binary_expression<L, Operator, R>>
-  {
-    using type = bool;
-  };
+  struct requires_braces<logical_expression<L, Operator, R>> : public std::true_type{};
 
-  template <typename L, typename Operator, typename R>
-  constexpr auto requires_braces_v<logical_binary_expression<L, Operator, R>> = true;
-
-  template <typename Context, typename L, typename Operator, typename R>
-  [[nodiscard]] auto to_sql_string(Context& context, const logical_binary_expression<L, Operator, R>& t)
-  {
-    return to_sql_string(context, embrace(t._l)) + Operator::symbol + to_sql_string(context, embrace(t._r));
-  }
-
-  template <typename Context, typename Operator, typename R>
-  [[nodiscard]] auto to_sql_string(Context& context, const logical_binary_expression<none_t, Operator, R>& t)
-  {
-    return Operator::symbol + to_sql_string(context, embrace(t._r));
-  }
-
-  template <typename Context, typename L1, typename Operator, typename R1, typename R2>
-  [[nodiscard]] auto to_sql_string(Context& context, const logical_binary_expression<logical_binary_expression<L1, Operator, R1>, Operator, R2>& t)
-  {
-    return to_sql_string(context, t._l) + Operator::symbol + to_sql_string(context, embrace(t._r));
-  }
-  */
   template <typename Context, typename L, typename Operator, typename R>
   auto serialize_impl(Context& context, const logical_expression<L, Operator, R>& t) -> Context&
   {
-    context << "(";
     serialize_operand(context, t._l);
     context << Operator::symbol;
     serialize_operand(context, t._r);
-    context << ")";
     return context;
   }
-  
+
   template <typename Context, typename L, typename Operator, typename R>
   auto serialize(Context& context, const logical_expression<L, Operator, R>& t) -> Context&
   {
diff --git a/include/sqlpp11/core/operator/sort_order_expression.h b/include/sqlpp11/core/operator/sort_order_expression.h
index f73178e7..6c2f07d0 100644
--- a/include/sqlpp11/core/operator/sort_order_expression.h
+++ b/include/sqlpp11/core/operator/sort_order_expression.h
@@ -66,24 +66,6 @@ namespace sqlpp
   template <typename L>
   struct is_sort_order<sort_order_expression<L>> : std::true_type {};
 
-  /*
-  template <typename L>
-  constexpr auto requires_braces_v<sort_order_t<L>> = false;
-
-  template <typename Context>
-  [[nodiscard]] auto to_sql_string(Context& context, const sort_type& t)
-  {
-    switch (t)
-    {
-      case sort_type::asc:
-        return std::string(" ASC");
-      case sort_type::desc:
-        return std::string(" DESC");
-    }
-  }
-
-  */
-
   template <typename Context>
   auto serialize(Context& context, const sort_type& t) -> Context&
   {
diff --git a/include/sqlpp11/core/type_traits.h b/include/sqlpp11/core/type_traits.h
index 9ebdc787..14bbf159 100644
--- a/include/sqlpp11/core/type_traits.h
+++ b/include/sqlpp11/core/type_traits.h
@@ -843,6 +843,10 @@ namespace sqlpp
   template <typename Statement, template <typename> class Predicate>
   using has_policy_t = typename has_policy_impl<Statement, Predicate>::type;
 
+#warning rename to requires_parentheses
+  template<typename T>
+  struct requires_braces : public std::false_type {};
+
   struct no_context_t
   {
   };
@@ -861,7 +865,6 @@ namespace sqlpp
   template <typename T>
     struct is_sort_order : public std::false_type {};
 
-
   template <typename Db>
   using serializer_context_of = typename serializer_context_of_impl<Db>::type;
 }  // namespace sqlpp
diff --git a/tests/core/serialize/Any.cpp b/tests/core/serialize/Any.cpp
deleted file mode 100644
index f46dbbfb..00000000
--- a/tests/core/serialize/Any.cpp
+++ /dev/null
@@ -1,42 +0,0 @@
-/*
- * Copyright (c) 2023, Roland Bock
- * All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without modification,
- * are permitted provided that the following conditions are met:
- *
- *  * Redistributions of source code must retain the above copyright notice,
- *    this list of conditions and the following disclaimer.
- *  * Redistributions in binary form must reproduce the above copyright notice,
- *    this list of conditions and the following disclaimer in the documentation
- *    and/or other materials provided with the distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
- * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
- * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
- * IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
- * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
- * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
- * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
- * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
- * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
- * OF THE POSSIBILITY OF SUCH DAMAGE.
- */
-
-#include "Sample.h"
-#include "compare.h"
-#include <sqlpp11/sqlpp11.h>
-
-int Any(int, char* [])
-{
-  const auto bar = test::TabBar{};
-
-  // With sub select.
-  static_assert(sqlpp::is_table<test::TabBar>::value, "");
-  compare(__LINE__, any(select(bar.id).from(bar).where(bar.id > 17)),
-          "ANY(SELECT tab_bar.id FROM tab_bar WHERE (tab_bar.id > 17))");
-  compare(__LINE__, bar.intN == any(select(bar.id).from(bar).where(bar.id > 17)),
-          "(tab_bar.int_n = ANY(SELECT tab_bar.id FROM tab_bar WHERE (tab_bar.id > 17)))");
-
-  return 0;
-}
diff --git a/tests/core/serialize/CMakeLists.txt b/tests/core/serialize/CMakeLists.txt
index 4c2f4e86..794ccb8a 100644
--- a/tests/core/serialize/CMakeLists.txt
+++ b/tests/core/serialize/CMakeLists.txt
@@ -24,7 +24,6 @@
 
 set(test_files
     logical_expression.cpp
-    Any.cpp
     As.cpp
     Avg.cpp
     Blob.cpp
@@ -66,3 +65,5 @@ foreach(test_file IN LISTS test_files)
         COMMAND sqlpp11_core_serialize ${test}
     )
 endforeach()
+
+add_subdirectory(operator)
diff --git a/tests/core/types/operator/CMakeLists.txt b/tests/core/types/operator/CMakeLists.txt
index b56e1f45..ab4791ae 100644
--- a/tests/core/types/operator/CMakeLists.txt
+++ b/tests/core/types/operator/CMakeLists.txt
@@ -23,7 +23,7 @@
 # SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 function(test_compile name)
-    set(target sqlpp11_types_operator_${name})
+    set(target sqlpp11_core_types_operator_${name})
     add_executable(${target} ${name}.cpp)
     target_link_libraries(${target} PRIVATE sqlpp11::sqlpp11 sqlpp11_testing)
 endfunction()