diff --git a/source/adios2/CMakeLists.txt b/source/adios2/CMakeLists.txt
index ff1645b4bb..5bc3f9c121 100644
--- a/source/adios2/CMakeLists.txt
+++ b/source/adios2/CMakeLists.txt
@@ -133,8 +133,7 @@ if (ADIOS2_HAVE_Derived_Variable)
   target_sources(adios2_core PRIVATE
       core/VariableDerived.cpp
       toolkit/derived/Expression.cpp
-      toolkit/derived/Function.cpp toolkit/derived/Function.tcc
-      toolkit/derived/ExprHelper.h)
+      toolkit/derived/Function.cpp toolkit/derived/Function.tcc)
   set_target_properties(adios2_core PROPERTIES
   				   INCLUDE_DIRECTORIES "$<BUILD_INTERFACE:${ADIOS2_SOURCE_DIR}/source/adios2/toolkit/derived/parser>;$<BUILD_INTERFACE:${ADIOS2_BINARY_DIR}/source/adios2>")
   find_package(BISON "3.8.2")
diff --git a/source/adios2/core/VariableDerived.h b/source/adios2/core/VariableDerived.h
index cc7bf8cbf2..f0185f45c2 100644
--- a/source/adios2/core/VariableDerived.h
+++ b/source/adios2/core/VariableDerived.h
@@ -1,9 +1,7 @@
 #ifndef ADIOS2_CORE_VARIABLE_DERIVED_H_
 #define ADIOS2_CORE_VARIABLE_DERIVED_H_
 
-#include "adios2/common/ADIOSTypes.h"
 #include "adios2/core/VariableBase.h"
-#include "adios2/helper/adiosType.h"
 #include "adios2/toolkit/derived/Expression.h"
 
 namespace adios2
diff --git a/source/adios2/toolkit/derived/DerivedData.h b/source/adios2/toolkit/derived/DerivedData.h
new file mode 100644
index 0000000000..30365ebd05
--- /dev/null
+++ b/source/adios2/toolkit/derived/DerivedData.h
@@ -0,0 +1,18 @@
+#ifndef ADIOS2_DERIVED_Data_H_
+#define ADIOS2_DERIVED_Data_H_
+
+#include "adios2/common/ADIOSTypes.h"
+
+namespace adios2
+{
+namespace derived
+{
+struct DerivedData
+{
+    void *Data;
+    Dims Start;
+    Dims Count;
+};
+}
+}
+#endif
diff --git a/source/adios2/toolkit/derived/ExprHelper.h b/source/adios2/toolkit/derived/ExprHelper.h
deleted file mode 100644
index 38672cfec4..0000000000
--- a/source/adios2/toolkit/derived/ExprHelper.h
+++ /dev/null
@@ -1,63 +0,0 @@
-#ifndef ADIOS2_DERIVED_PARSER_EXPHELPER_H_
-#define ADIOS2_DERIVED_PARSER_EXPHELPER_H_
-
-#include <map>
-#include <string>
-#include <tuple>
-#include <vector>
-
-namespace adios2
-{
-namespace detail
-{
-
-enum ExpressionOperator
-{
-    OP_NULL,
-    OP_ALIAS, /* Parser-use only */
-    OP_PATH,  /* Parser-use only */
-    OP_NUM,   /* Parser-use only */
-    OP_INDEX,
-    OP_ADD,
-    OP_SQRT,
-    OP_POW,
-    OP_MAGN,
-    OP_CURL
-};
-
-struct OperatorProperty
-{
-    std::string name;
-    bool is_associative;
-};
-
-const std::map<ExpressionOperator, OperatorProperty> op_property = {
-    {ExpressionOperator::OP_NULL, {"NULL", false}},
-    {ExpressionOperator::OP_ALIAS, {"ALIAS", false}}, /* Parser-use only */
-    {ExpressionOperator::OP_PATH, {"PATH", false}},   /* Parser-use only */
-    {ExpressionOperator::OP_NUM, {"NUM", false}},     /* Parser-use only */
-    {ExpressionOperator::OP_INDEX, {"INDEX", false}},
-    {ExpressionOperator::OP_ADD, {"ADD", true}},
-    {ExpressionOperator::OP_SQRT, {"SQRT", false}},
-    {ExpressionOperator::OP_POW, {"POW", false}},
-    {ExpressionOperator::OP_CURL, {"CURL", false}},
-    {ExpressionOperator::OP_MAGN, {"MAGNITUDE", false}}};
-
-const std::map<std::string, ExpressionOperator> string_to_op = {
-    {"ALIAS", ExpressionOperator::OP_ALIAS}, /* Parser-use only */
-    {"PATH", ExpressionOperator::OP_PATH},   /* Parser-use only */
-    {"NUM", ExpressionOperator::OP_NUM},     /* Parser-use only */
-    {"INDEX", ExpressionOperator::OP_INDEX},    {"+", ExpressionOperator::OP_ADD},
-    {"add", ExpressionOperator::OP_ADD},        {"ADD", ExpressionOperator::OP_ADD},
-    {"SQRT", ExpressionOperator::OP_SQRT},      {"sqrt", ExpressionOperator::OP_SQRT},
-    {"POW", ExpressionOperator::OP_POW},        {"^", ExpressionOperator::OP_POW},
-    {"CURL", ExpressionOperator::OP_CURL},      {"curl", ExpressionOperator::OP_CURL},
-    {"MAGNITUDE", ExpressionOperator::OP_MAGN}, {"magnitude", ExpressionOperator::OP_MAGN}};
-
-inline std::string get_op_name(ExpressionOperator op) { return op_property.at(op).name; }
-
-inline ExpressionOperator get_op(std::string op) { return string_to_op.at(op); }
-
-}
-}
-#endif
diff --git a/source/adios2/toolkit/derived/Expression.cpp b/source/adios2/toolkit/derived/Expression.cpp
index 81db7ccd15..89fa8083ac 100644
--- a/source/adios2/toolkit/derived/Expression.cpp
+++ b/source/adios2/toolkit/derived/Expression.cpp
@@ -2,14 +2,49 @@
 #define ADIOS2_DERIVED_Expression_CPP_
 
 #include "Expression.h"
+#include "Function.h"
+#include "adios2/helper/adiosLog.h"
 #include "parser/ASTDriver.h"
 
 namespace adios2
 {
 namespace detail
 {
+struct OperatorProperty
+{
+    std::string name;
+    bool is_associative;
+};
+
+const std::map<ExpressionOperator, OperatorProperty> op_property = {
+    {ExpressionOperator::OP_NULL, {"NULL", false}},
+    {ExpressionOperator::OP_ALIAS, {"ALIAS", false}}, /* Parser-use only */
+    {ExpressionOperator::OP_PATH, {"PATH", false}},   /* Parser-use only */
+    {ExpressionOperator::OP_NUM, {"NUM", false}},     /* Parser-use only */
+    {ExpressionOperator::OP_INDEX, {"INDEX", false}},
+    {ExpressionOperator::OP_ADD, {"ADD", true}},
+    {ExpressionOperator::OP_SQRT, {"SQRT", false}},
+    {ExpressionOperator::OP_POW, {"POW", false}},
+    {ExpressionOperator::OP_CURL, {"CURL", false}},
+    {ExpressionOperator::OP_MAGN, {"MAGNITUDE", false}}};
+
+const std::map<std::string, ExpressionOperator> string_to_op = {
+    {"ALIAS", ExpressionOperator::OP_ALIAS}, /* Parser-use only */
+    {"PATH", ExpressionOperator::OP_PATH},   /* Parser-use only */
+    {"NUM", ExpressionOperator::OP_NUM},     /* Parser-use only */
+    {"INDEX", ExpressionOperator::OP_INDEX},    {"+", ExpressionOperator::OP_ADD},
+    {"add", ExpressionOperator::OP_ADD},        {"ADD", ExpressionOperator::OP_ADD},
+    {"SQRT", ExpressionOperator::OP_SQRT},      {"sqrt", ExpressionOperator::OP_SQRT},
+    {"POW", ExpressionOperator::OP_POW},        {"^", ExpressionOperator::OP_POW},
+    {"CURL", ExpressionOperator::OP_CURL},      {"curl", ExpressionOperator::OP_CURL},
+    {"MAGNITUDE", ExpressionOperator::OP_MAGN}, {"magnitude", ExpressionOperator::OP_MAGN}};
+
+inline std::string get_op_name(ExpressionOperator op) { return op_property.at(op).name; }
+
+inline ExpressionOperator get_op(std::string op) { return string_to_op.at(op); }
+
 // helper function
-adios2::detail::ExpressionOperator convert_op(std::string opname)
+ExpressionOperator convert_op(std::string opname)
 {
     adios2::detail::ExpressionOperator op;
     try
@@ -77,6 +112,16 @@ adios2::derived::ExpressionTree ASTNode_to_ExpressionTree(adios2::detail::ASTNod
 
 namespace derived
 {
+struct OperatorFunctions
+{
+    std::function<DerivedData(std::vector<DerivedData>, DataType)> ComputeFct;
+    std::function<Dims(std::vector<Dims>)> DimsFct;
+};
+
+std::map<adios2::detail::ExpressionOperator, OperatorFunctions> OpFunctions = {
+    {adios2::detail::ExpressionOperator::OP_ADD, {AddFunc, SameDimsFunc}},
+    {adios2::detail::ExpressionOperator::OP_CURL, {Curl3DFunc, CurlDimsFunc}},
+    {adios2::detail::ExpressionOperator::OP_MAGN, {MagnitudeFunc, SameDimsFunc}}};
 
 Expression::Expression(std::string string_exp)
 : m_Shape({0}), m_Start({0}), m_Count({0}), ExprString(string_exp)
diff --git a/source/adios2/toolkit/derived/Expression.h b/source/adios2/toolkit/derived/Expression.h
index 2b6f8912a3..41118c631f 100644
--- a/source/adios2/toolkit/derived/Expression.h
+++ b/source/adios2/toolkit/derived/Expression.h
@@ -1,13 +1,28 @@
 #ifndef ADIOS2_DERIVED_Expression_H_
 #define ADIOS2_DERIVED_Expression_H_
 
-#include "Function.h"
-#include "adios2/common/ADIOSTypes.h"
+#include "DerivedData.h"
 #include <string>
 #include <unordered_map>
 
 namespace adios2
 {
+namespace detail
+{
+enum ExpressionOperator
+{
+    OP_NULL,
+    OP_ALIAS, /* Parser-use only */
+    OP_PATH,  /* Parser-use only */
+    OP_NUM,   /* Parser-use only */
+    OP_INDEX,
+    OP_ADD,
+    OP_SQRT,
+    OP_POW,
+    OP_MAGN,
+    OP_CURL
+};
+}
 
 namespace derived
 {
diff --git a/source/adios2/toolkit/derived/Function.cpp b/source/adios2/toolkit/derived/Function.cpp
index 7cb032f750..f6bc056543 100644
--- a/source/adios2/toolkit/derived/Function.cpp
+++ b/source/adios2/toolkit/derived/Function.cpp
@@ -3,8 +3,8 @@
 
 #include "Function.h"
 #include "Function.tcc"
-#include "adios2/common/ADIOSMacros.h"
 #include "adios2/helper/adiosFunctions.h"
+#include "adios2/helper/adiosLog.h"
 #include <adios2-perfstubs-interface.h>
 #include <cmath>
 
@@ -12,11 +12,6 @@ namespace adios2
 {
 namespace derived
 {
-std::map<adios2::detail::ExpressionOperator, OperatorFunctions> OpFunctions = {
-    {adios2::detail::ExpressionOperator::OP_ADD, {AddFunc, SameDimsFunc}},
-    {adios2::detail::ExpressionOperator::OP_CURL, {Curl3DFunc, CurlDimsFunc}},
-    {adios2::detail::ExpressionOperator::OP_MAGN, {MagnitudeFunc, SameDimsFunc}}};
-
 DerivedData AddFunc(std::vector<DerivedData> inputData, DataType type)
 {
     PERFSTUBS_SCOPED_TIMER("derived::Function::AddFunc");
diff --git a/source/adios2/toolkit/derived/Function.h b/source/adios2/toolkit/derived/Function.h
index 7554916851..b72270ac46 100644
--- a/source/adios2/toolkit/derived/Function.h
+++ b/source/adios2/toolkit/derived/Function.h
@@ -1,29 +1,12 @@
 #ifndef ADIOS2_DERIVED_Function_H_
 #define ADIOS2_DERIVED_Function_H_
 
-#include "ExprHelper.h"
-#include "adios2/common/ADIOSTypes.h"
-#include "adios2/helper/adiosLog.h"
-#include <functional>
+#include "DerivedData.h"
 
 namespace adios2
 {
 namespace derived
 {
-
-struct DerivedData
-{
-    void *Data;
-    Dims Start;
-    Dims Count;
-};
-
-struct OperatorFunctions
-{
-    std::function<DerivedData(std::vector<DerivedData>, DataType)> ComputeFct;
-    std::function<Dims(std::vector<Dims>)> DimsFct;
-};
-
 DerivedData AddFunc(std::vector<DerivedData> input, DataType type);
 DerivedData MagnitudeFunc(std::vector<DerivedData> input, DataType type);
 DerivedData Curl3DFunc(std::vector<DerivedData> input, DataType type);
@@ -33,13 +16,6 @@ T linear_interp(T *data, size_t index, size_t count, size_t stride = 1);
 
 Dims SameDimsFunc(std::vector<Dims> input);
 Dims CurlDimsFunc(std::vector<Dims> input);
-
-extern std::map<adios2::detail::ExpressionOperator, OperatorFunctions> OpFunctions;
-
-template <class T>
-T *ApplyOneToOne(std::vector<DerivedData> inputData, size_t dataSize,
-                 std::function<T(T, T)> compFct);
-
 }
 }
 #endif
diff --git a/source/adios2/toolkit/derived/Function.tcc b/source/adios2/toolkit/derived/Function.tcc
index 077ad1e933..e93dc2c909 100644
--- a/source/adios2/toolkit/derived/Function.tcc
+++ b/source/adios2/toolkit/derived/Function.tcc
@@ -2,6 +2,7 @@
 #define ADIOS2_DERIVED_Function_TCC_
 
 #include "Function.h"
+#include "adios2/helper/adiosLog.h"
 #include <algorithm>
 #include <cstring>
 #include <iostream>