diff --git a/src/core/common_code/common_code.h b/src/core/common_code/common_code.h
index 0d096e2..4a935fa 100644
--- a/src/core/common_code/common_code.h
+++ b/src/core/common_code/common_code.h
@@ -139,18 +139,20 @@ public:
     // ------------------------------------------------------------------------------------- //
 
     /// Compare CommonCode with u64 values.
-    friend constexpr auto operator==(const CommonCode &c1, uint64_t c2);
-    friend constexpr auto operator<=>(const CommonCode &c1, uint64_t c2);
+    friend constexpr auto operator==(const CommonCode &lhs, uint64_t rhs);
+    friend constexpr auto operator<=>(const CommonCode &lhs, uint64_t rhs);
 
     /// Compare the original values of two CommonCodes.
-    friend constexpr auto operator==(const CommonCode &c1, const CommonCode &c2);
-    friend constexpr auto operator<=>(const CommonCode &c1, const CommonCode &c2);
+    friend constexpr auto operator==(const CommonCode &lhs, const CommonCode &rhs);
+    friend constexpr auto operator<=>(const CommonCode &lhs, const CommonCode &rhs);
 
     // ------------------------------------------------------------------------------------- //
 
 private:
     uint64_t code_;
 
+    // ------------------------------------------------------------------------------------- //
+
     /// Serialize CommonCode into a 9-bit length string.
     static std::string string_encode(uint64_t common_code);
 
@@ -159,6 +161,8 @@ private:
 
     /// Deserialize CommonCode from string and return std::nullopt on error.
     static std::optional<uint64_t> string_decode(const std::string &common_code);
+
+    // ------------------------------------------------------------------------------------- //
 };
 
 } // namespace klotski::codec
diff --git a/src/core/common_code/internal/common_code.inl b/src/core/common_code/internal/common_code.inl
index 90b1a65..b7907e1 100644
--- a/src/core/common_code/internal/common_code.inl
+++ b/src/core/common_code/internal/common_code.inl
@@ -21,20 +21,20 @@ inline std::ostream& operator<<(std::ostream &out, const CommonCode self) {
 
 // ------------------------------------------------------------------------------------- //
 
-constexpr auto operator==(const CommonCode &c1, const uint64_t c2) {
-    return c1.code_ == c2;
+constexpr auto operator==(const CommonCode &lhs, const uint64_t rhs) {
+    return lhs.code_ == rhs;
 }
 
-constexpr auto operator<=>(const CommonCode &c1, const uint64_t c2) {
-    return c1.code_ <=> c2;
+constexpr auto operator<=>(const CommonCode &lhs, const uint64_t rhs) {
+    return lhs.code_ <=> rhs;
 }
 
-constexpr auto operator==(const CommonCode &c1, const CommonCode &c2) {
-    return c1.code_ == c2.code_;
+constexpr auto operator==(const CommonCode &lhs, const CommonCode &rhs) {
+    return lhs.code_ == rhs.code_;
 }
 
-constexpr auto operator<=>(const CommonCode &c1, const CommonCode &c2) {
-    return c1.code_ <=> c2.code_;
+constexpr auto operator<=>(const CommonCode &lhs, const CommonCode &rhs) {
+    return lhs.code_ <=> rhs.code_;
 }
 
 // ------------------------------------------------------------------------------------- //