diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index d214276..8cd5289 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -14,7 +14,8 @@ add_subdirectory(raw_code)
 add_subdirectory(short_code)
 add_subdirectory(common_code)
 
-add_executable(klotski main.cc)
+#add_executable(klotski main.cc)
+add_executable(klotski main.cc core_demo.cc)
 target_link_libraries(klotski all_cases)
 
 target_link_libraries(klotski raw_code)
diff --git a/src/common_code/common_code.h b/src/common_code/common_code.h
index 79d66d1..928bb50 100644
--- a/src/common_code/common_code.h
+++ b/src/common_code/common_code.h
@@ -9,16 +9,19 @@ class ShortCode;
 class CommonCode {
 public:
     uint64_t unwrap() const;
-    ShortCode to_short_code() const;
     static bool check(uint64_t common_code);
     static CommonCode unsafe_create(uint64_t code);
+
+    // TODO: to raw code function
+    ShortCode to_short_code() const;
     std::string to_string(bool shorten = false) const;
 
     explicit CommonCode(uint64_t common_code);
+    // TODO: init with const RawCode&
     explicit CommonCode(const ShortCode &short_code);
     explicit CommonCode(const std::string &common_code_str);
 
 private:
     uint64_t code;
-    CommonCode() = default;
+    CommonCode() = default; // unsafe init
 };
diff --git a/src/core_demo.cc b/src/core_demo.cc
new file mode 100644
index 0000000..069c573
--- /dev/null
+++ b/src/core_demo.cc
@@ -0,0 +1,9 @@
+#include <iostream>
+#include "raw_code.h"
+
+void next_step(uint64_t raw_code, uint64_t mask) {
+
+    std::cout << RawCode(raw_code).dump_case();
+    printf("mask -> %016lX\n", mask);
+
+}
diff --git a/src/core_demo.h b/src/core_demo.h
new file mode 100644
index 0000000..19ded5c
--- /dev/null
+++ b/src/core_demo.h
@@ -0,0 +1,5 @@
+#pragma once
+
+#include <cstdint>
+
+void next_step(uint64_t raw_code, uint64_t mask);
diff --git a/src/main.cc b/src/main.cc
index 9360703..54dd94b 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -5,6 +5,8 @@
 #include "short_code.h"
 #include "raw_code.h"
 
+#include "core_demo.h"
+
 #include <thread>
 
 //void get_status() {
@@ -134,8 +136,11 @@ int main() {
 //    printf("%015lX\n", RawCode(CommonCode(0x4FEA13400)).unwrap());
 
 //    auto r = RawCode(0x0E58FC85FFEBC4DB);
-    auto r = RawCode(0x0E58FC85FFEBC4DD);
-    std::cout << r.dump_case() << std::endl;
+//    auto r = RawCode(0x0E58FC85FFEBC4DD); // invalid raw code -> only for test
+//    std::cout << r.dump_case() << std::endl;
+
+
+    next_step(0x0E58FC85FFEBC4DB, 0); // mask unset
 
     return 0;
 }