fix a bug in XLink::MakeLink

source/tensor/XLink.cpp

@@ -321,7 +321,7 @@ void XLink::MakeLink(const XList * list, XTensor * h, int id)
             continue;
         XLink &outgo = t->outgo;
         CheckNTErrors(outgo.head == NULL || outgo.head == t, 
-                      "Wrong head of the hyperedge!");
+                     "Wrong head of the hyperedge!");
         outgo.SetHead(t);
         outgo.AddTail(h);
     }
@@ -349,6 +349,7 @@ void XLink::MakeLink(XTensor * t, XList * list, int id)
 
     /* backward */
     XLink &outgo = t->outgo;
+    outgo.SetHead(t);
     CheckNTErrors(outgo.head == NULL || outgo.head == t, "Wrong head of the hyperedge!");
     for(int i = 0; i < list->count; i++){
         XTensor * t = (XTensor*)list->GetItem(i);