diff --git a/src/block.cc b/src/block.cc
index a351545..8ad4f19 100644
--- a/src/block.cc
+++ b/src/block.cc
@@ -32,6 +32,7 @@ namespace MultiArrayHelper
 	static OpFunc f;
 	if(mRes.size() == 0) { mRes.assign(arg.size(), static_cast<T>(0)); }
 	assert(mRes.size() == arg.size());
+	VCHECK(arg);
 	for(size_t i = 0; i != arg.size(); ++i){
 	    mRes[i] = f(mRes[i], arg[i]);
 	}
diff --git a/src/block.h b/src/block.h
index ffb6610..e007350 100644
--- a/src/block.h
+++ b/src/block.h
@@ -56,7 +56,7 @@ namespace MultiArrayHelper
     };
 
     template <typename T>
-    std::ostream& operator<<(std::ostream& out, const BlockBase<T>& block)
+    std::ostream& operator<<(std::ostream& out, const MBlock<T>& block)
     {
 	out << block[0];
 	for(size_t i = 1; i != block.size(); ++i){
@@ -64,6 +64,17 @@ namespace MultiArrayHelper
 	}
 	return out;
     }
+
+    template <typename T>
+    std::ostream& operator<<(std::ostream& out, const BlockResult<T>& block)
+    {
+	out << block[0];
+	for(size_t i = 1; i != block.size(); ++i){
+	    out << ", " << block[i];
+	}
+	return out;
+    }
+
     
     template <typename T>
     class MutableBlockBase : public BlockBase<T>
diff --git a/src/multi_array_operation.cc b/src/multi_array_operation.cc
index 647e882..54bee2c 100644
--- a/src/multi_array_operation.cc
+++ b/src/multi_array_operation.cc
@@ -355,8 +355,9 @@ namespace MultiArrayTools
     template <typename T, class Op, class IndexType>
     const BlockResult<T>& Contraction<T,Op,IndexType>::get() const
     {
-	BlockBinaryOpSelf<T,std::plus<T>,BlockResult<T> > f(mRes);
+	BlockBinaryOpSelf<T,std::plus<T>,decltype(mOp.get())> f(mRes);
 	for(*mInd = 0; mInd->pos() != mInd->max(); ++(*mInd)){
+	    VCHECK(mInd->pos());
 	    f(mOp.get());
 	}
 	return mRes;