diff --git a/04_UDEF/MP/main_04_UDEF_e.cpp b/04_UDEF/MP/main_04_UDEF_e.cpp
index d29b19c..cc84326 100644
--- a/04_UDEF/MP/main_04_UDEF_e.cpp
+++ b/04_UDEF/MP/main_04_UDEF_e.cpp
@@ -13,6 +13,7 @@ public:
     BinaryOctet(const BinaryOctet &) = default;
     BinaryOctet &operator=(int const &a);
     const BinaryOctet operator--(int);
+    const BinaryOctet operator-(BinaryOctet a);
     const BinaryOctet operator+(BinaryOctet a);
 };
 
@@ -25,6 +26,9 @@ BinaryOctet::BinaryOctet() {
 
 
 BinaryOctet::BinaryOctet(int x) {
+    for (char &bitsAsDigit : bitsAsDigits) {
+        bitsAsDigit = '0';
+    }
     for (int i = 0; i <= bitsPerOctet - 1; i++) {
         int tmp = ((x >> i) & 1);
         bitsAsDigits[i] = (tmp == 1) ? '1' : '0';
@@ -53,16 +57,23 @@ bool operator!=(BinaryOctet a, BinaryOctet b) {
 
 //TODO: this method
 const BinaryOctet BinaryOctet::operator--(const int) {
-    bool over = false;
-    for(int i = bitsPerOctet - 1; i >= 0; --i) {
-        int tmp = bitsAsDigits[i] - '0';
+    return operator-(1);
+}
 
-
-
-        bitsAsDigits[i] = static_cast<char>(tmp + '0');
+//FIXME: returns wrong result
+//using complement method here
+const BinaryOctet BinaryOctet::operator-(BinaryOctet a) {
+    BinaryOctet result;
+    //reverse a
+    for(int i = 0; i <= bitsPerOctet; i++) {
+        a.bitsAsDigits[i] = a.bitsAsDigits[i] == '0' ? '1' : '0';
     }
+    a + 1;
 
-    return *this;
+    result = *this + a;
+    std::cout << result.evenParity << std::endl;
+
+    return result;
 }
 
 
@@ -157,15 +168,28 @@ std::ostream &operator<<(std::ostream &os, BinaryOctet *toBePrinted) {
 
 
 int main(int argc, char **argv) {
-    BinaryOctet a = 0b00001111;
-    std::cout << a << std::endl;
-    BinaryOctet b = 0b00000110;
-    std::cout << b << std::endl;
-    b--;
-    std::cout << b << std::endl;
+
+    std::cout << "=========   init   ==========" << std::endl;
+    BinaryOctet a = 0b00001111; //15
+    std::cout << "a = " << a << std::endl;
+    BinaryOctet b = 0b00000110;//6
+    std::cout << "b = " << b << std::endl;
     auto *c = new BinaryOctet(5);
-    std::cout << c << std::endl;
-    std::cout << a + b << std::endl;
+    std::cout << "c = " << c << std::endl;
+
+    std::cout << "========   operator+   ===========" <<std::endl;
+    std::cout << "a + b = " << a + b << std::endl;
+
+    std::cout << "=========   operator-   ==========" << std::endl;
+    std::cout << "a - b = " << a - b << std::endl;
+
+
+    std::cout << "========   operator--   ============" << std::endl;
+    BinaryOctet d = 0b111111111;
+    d--;
+    std::cout << d-- << std::endl;
+
+    std::cout << "==============   doCalculation   ================" << std::endl;
     std::cout << "result = " << doCalculation(a, b) << std::endl;
     return 0;
 }