diff --git a/CPlusPlus20ForProgrammers-master/examples/ch06/a.out b/CPlusPlus20ForProgrammers-master/examples/ch06/a.out
index f625659..ed9afff 100755
Binary files a/CPlusPlus20ForProgrammers-master/examples/ch06/a.out and b/CPlusPlus20ForProgrammers-master/examples/ch06/a.out differ
diff --git a/CPlusPlus20ForProgrammers-master/examples/ch06/matrix.cpp b/CPlusPlus20ForProgrammers-master/examples/ch06/matrix.cpp
index a17ee65..23576aa 100644
--- a/CPlusPlus20ForProgrammers-master/examples/ch06/matrix.cpp
+++ b/CPlusPlus20ForProgrammers-master/examples/ch06/matrix.cpp
@@ -1,9 +1,36 @@
 #include <iostream>
 #include <array>
 #include <vector>
+#include <concepts>
+
+
+// abbreviated function template with constrained auto
 
 constexpr size_t rows{4};
 constexpr size_t columns{4};
+
+
+auto Dot(auto& V, auto& B) {
+        auto tmp {V[0]*B[0]};
+        for (int i{1}; i < B.size(); i++)
+                 tmp+= B[i] * V[i];
+        return tmp;
+}
+
+
+void MatVecMul_auto(const auto& A, const auto & V, auto& B){
+    if (A[0].size() == V.size() && A.size() == B.size() ){
+     for (int i{0}; i < A.size(); i++)
+        for (int j{0}; j < A[0].size(); j++)
+             B[i]+= A[i][j] * V[j];
+    }
+    else{
+        std::cout << "sizes are not compatible!";
+    }
+}
+
+
+
 void MatVecMul(const std::array<std::array<int, columns>, rows>& A, const std::array<int,columns>& V, std::array<int,rows>& B);
 
 template <typename T, long unsigned int N>
@@ -17,10 +44,10 @@ void printArrayTemplate(const T& a);
 
 int main() {
     std::array A{std::array{1, 2, 3}, std::array{4, 5, 6},std::array{4, 5, 0}};
-    std::array V{1, 2, 3,5};
+    std::array V{1, 2, 3 };
     std::array <int,3> B{};
     MatVecMul_template(A, B, V);
-
+    Dot(B,V);
    return 0;
 }
 
@@ -54,4 +81,5 @@ void MatVecMul_templatefull(const T& A, const U& V, U& B){
     else{
         std::cout << "sizes are not compatible!";
     }
-}
\ No newline at end of file
+}
+