diff --git a/src/include/dynamic_operation.cc.h b/src/include/dynamic_operation.cc.h
index 020ad4e..056628d 100644
--- a/src/include/dynamic_operation.cc.h
+++ b/src/include/dynamic_operation.cc.h
@@ -4,7 +4,7 @@
 namespace MultiArrayTools
 {
     template <typename T, class Operation>
-    const T& DynamicOperation<T,Operation>::get(const DExtT& pos) const
+    T DynamicOperation<T,Operation>::get(const DExtT& pos) const
     {
 	return mOp.get(pos.expl<ET>());
     }
diff --git a/src/include/dynamic_operation.h b/src/include/dynamic_operation.h
index 4982333..704b3a6 100644
--- a/src/include/dynamic_operation.h
+++ b/src/include/dynamic_operation.h
@@ -24,7 +24,7 @@ namespace MultiArrayTools
 	DynamicOperationBase& operator=(const DynamicOperationBase& in) = default;
 	DynamicOperationBase& operator=(DynamicOperationBase&& in) = default;
 
-	virtual const T& get(const DExtT& pos) const = 0;
+	virtual T get(const DExtT& pos) const = 0;
 	virtual DynamicOperationBase& set(const DExtT& pos) = 0;
 	virtual DExtT rootSteps(std::intptr_t iPtrNum = 0) const = 0;
 	virtual DynamicExpression loop(const DynamicExpression& exp) const = 0;
@@ -50,7 +50,7 @@ namespace MultiArrayTools
 
 	DynamicOperation(const Operation& op) : mOp(op) {}
 
-	virtual const T& get(const DExtT& pos) const override final;
+	virtual T get(const DExtT& pos) const override final;
 	virtual DynamicOperationBase<T>& set(const DExtT& pos) override final;
 	virtual DExtT rootSteps(std::intptr_t iPtrNum = 0) const override final;
 	virtual DynamicExpression loop(const DynamicExpression& exp) const override final;
@@ -81,8 +81,9 @@ namespace MultiArrayTools
 	DynamicO(const Op& op) : mOp(std::make_shared<DynamicOperation<T,Op>>(op)) {}
 
         template <class X>
-	inline const T& get(const DExtTX<X>& pos) const { return mOp->get(pos.reduce()); }
-	inline DynamicO& set(const DExtT& pos) { return mOp->set(pos); }
+	inline T get(const DExtTX<X>& pos) const { return mOp->get(pos.reduce()); }
+        template <class X>
+	inline DynamicO& set(const DExtTX<X>& pos) { mOp->set(pos.reduce()); return *this; }
 	inline DExtT rootSteps(std::intptr_t iPtrNum = 0) const { return mOp->rootSteps(iPtrNum); }
 	inline DynamicExpression loop(const DynamicExpression& exp) const { return mOp->loop(exp); }
 	inline const T* data() const { return mOp->data(); }
diff --git a/src/include/multi_array_operation.cc.h b/src/include/multi_array_operation.cc.h
index 5e1199c..337ce0f 100644
--- a/src/include/multi_array_operation.cc.h
+++ b/src/include/multi_array_operation.cc.h
@@ -753,7 +753,8 @@ namespace MultiArrayTools
     template <class ET>
     inline Operation<T,OpFunction,Ops...>& Operation<T,OpFunction,Ops...>::set(ET pos)
     {
-	PackNum<sizeof...(Ops)-1>::setOpPos(mOps,pos);
+	typedef std::tuple<Ops...> OpTuple;
+	PackNum<sizeof...(Ops)-1>::template setOpPos<SIZE,OpTuple,ET>(mOps,pos);
 	return *this;
     }
 
diff --git a/src/include/multi_array_operation.h b/src/include/multi_array_operation.h
index 5ba3b1d..2301996 100644
--- a/src/include/multi_array_operation.h
+++ b/src/include/multi_array_operation.h
@@ -529,7 +529,8 @@ namespace MultiArrayTools
 	template <class Expr>
 	auto loop(Expr exp) const
 	    -> decltype(PackNum<sizeof...(Ops)-1>::mkLoop( mOps, exp));
-	
+
+	T* data() const { assert(0); return nullptr; }
     };
 
     namespace
diff --git a/src/include/pack_num.h b/src/include/pack_num.h
index 2797243..aa7f60a 100644
--- a/src/include/pack_num.h
+++ b/src/include/pack_num.h
@@ -122,7 +122,7 @@ namespace MultiArrayHelper
 	    static_assert(LAST > NextOpType::SIZE, "inconsistent array positions");
 	    static constexpr size_t NEXT = LAST - NextOpType::SIZE;
 	    std::get<N>( ot ).set( Getter<NEXT>::template getX<ETuple>( et ) );
-	    PackNum<N-1>::template setOpPos<NEXT>(ot, et);
+	    PackNum<N-1>::template setOpPos<NEXT,OpTuple,ETuple>(ot, et);
 	}
     };
     
@@ -205,9 +205,9 @@ namespace MultiArrayHelper
 	template <size_t LAST,class OpTuple, class ETuple>
 	static inline void setOpPos(OpTuple& ot, const ETuple& et)
 	{
-	    typedef typename std::remove_reference<decltype(std::get<0>(et))>::type NextOpType;
-	    static_assert(LAST > NextOpType::SIZE, "inconsistent array positions");
+	    typedef typename std::remove_reference<decltype(std::get<0>(ot))>::type NextOpType;
 	    static constexpr size_t NEXT = LAST - NextOpType::SIZE;
+	    static_assert(NEXT == 0, "inconsistent array positions");
 	    std::get<0>( ot ).set( Getter<NEXT>::template getX<ETuple>( et ) );
 	}
 
diff --git a/src/tests/op4_unit_test.cc b/src/tests/op4_unit_test.cc
index 4623943..7c9a973 100644
--- a/src/tests/op4_unit_test.cc
+++ b/src/tests/op4_unit_test.cc
@@ -104,10 +104,13 @@ namespace
 	(*di4)({imap["i2_1"],imap["i3_1"],imap["i4_1"],imap["i4_2"]});
 
 	auto resx1 = res1;
+	auto resx2 = res1;
+	auto resx3 = res1;
 	res1(i1,di4) = ma1(i1,di1) * ma2(i1,di2);
-
 	resx1(i1,di4) = mkDynOp(ma1(i1,di1)) * mkDynOp(ma2(i1,di2));
-	
+        resx2(i1,di4) = mkDynOp(ma1(i1,di1) * ma2(i1,di2));
+	resx3(i1,di4) = mkDynOp(mkDynOp(ma1(i1,di1)) * mkDynOp(ma2(i1,di2)));
+        
 	auto i2_1 = imap.at("i2_1");
 	auto i2_2 = imap.at("i2_2");
 	auto i3_1 = imap.at("i3_1");
@@ -123,10 +126,15 @@ namespace
 			    const size_t jr = (((ii1*i2_1->max() + ii2_1)*i3_1->max() + ii3_1)*i4_1->max() + ii4_1)*i4_2->max() + ii4_2;
 			    const size_t j1 = (((ii1*i2_1->max() + ii2_1)*i2_2->max() + ii2_2)*i3_1->max() + ii3_1)*i4_1->max() + ii4_1;
 			    const size_t j2 = ((ii1*i3_1->max() + ii3_1)*i3_1->max() + ii3_1)*i4_2->max() + ii4_2;
-			    auto resx = xround(res1.vdata()[jr]);
-			    //std::cout << resx << "  ";
-			    auto x12 = xround(ma1.vdata()[j1]*ma2.vdata()[j2]);
-			    EXPECT_EQ( resx, x12 );
+			    auto resv = xround(res1.vdata()[jr]);
+			    auto resx1v = xround(resx1.vdata()[jr]);
+			    auto resx2v = xround(resx2.vdata()[jr]);
+			    auto resx3v = xround(resx3.vdata()[jr]);
+	 		    auto x12 = xround(ma1.vdata()[j1]*ma2.vdata()[j2]);
+			    EXPECT_EQ( resv, x12 );
+			    EXPECT_EQ( resx1v, x12 );
+			    EXPECT_EQ( resx2v, x12 );
+			    EXPECT_EQ( resx3v, x12 );
 			}
 		    }
 		}