--- Ex.13.java	2007-05-29 20:17:37.000000000 +0100
+++ Ex.14.java	2007-05-29 20:19:01.000000000 +0100
@@ -31,6 +31,9 @@
     for (i = 0; i < r.length; ++i) s+=r[i];
     //@ assert r.length == pubs.length;
     //@ assert s >= 0;
+    int pc = 1;
+    for (i = 0; i < pubs.length; ++i) if (r[i] != 0) ++pc;
+    //@ assert pc > 0;
     return pubs.length == 0? 0 : s / pubs.length;
   }
 }