- Ignoring singular variables seems to be a smart choice, although it

implies that the intruder can generate any type. That is not conform
  the usual semantics. So we either change the usual semantics (wise) or
  we make this choice optional.

src/arachne.c

@@ -1035,7 +1035,10 @@ select_goal ()
       Binding b;
 
       b = (Binding) bl->data;
-      if (!b->done)
+
+      // Ignore singular variables
+      if (!b->done && !realTermVariable (deVar(b->term)) )
+      //if (!b->done)
 	{
 	  float cons;