diff --git a/vvp/arith.cc b/vvp/arith.cc
index 2a0b5dd1d..7a5e5f565 100644
--- a/vvp/arith.cc
+++ b/vvp/arith.cc
@@ -17,7 +17,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #ifdef HAVE_CVS_IDENT
-#ident "$Id: arith.cc,v 1.36 2005/01/28 05:34:25 steve Exp $"
+#ident "$Id: arith.cc,v 1.37 2005/01/30 05:06:49 steve Exp $"
 #endif
 
 # include  "arith.h"
@@ -361,10 +361,10 @@ vvp_arith_sub::~vvp_arith_sub()
 }
 
 /*
- * Subtraction works by adding the 2s complement of the B, C and D
- * inputs from the A input. The 2s complement is the 1s complement
- * plus one, so we further reduce the operation to adding in the
- * inverted value and adding a correction.
+ * Subtraction works by adding the 2s complement of the B input from
+ * the A input. The 2s complement is the 1s complement plus one, so we
+ * further reduce the operation to adding in the inverted value and
+ * adding a correction.
  */
 void vvp_arith_sub::recv_vec4(vvp_net_ptr_t ptr, vvp_vector4_t bit)
 {
@@ -381,7 +381,7 @@ void vvp_arith_sub::recv_vec4(vvp_net_ptr_t ptr, vvp_vector4_t bit)
       vvp_bit4_t carry = BIT4_1;
       for (unsigned idx = 0 ;  idx < wid_ ;  idx += 1) {
 	    vvp_bit4_t a = (idx >= op_a_.size())? pad : op_a_.value(idx);
-	    vvp_bit4_t b = (idx >= op_b_.size())? pad : op_b_.value(idx);
+	    vvp_bit4_t b = (idx >= op_b_.size())? pad : ~op_b_.value(idx);
 	    vvp_bit4_t cur = add_with_carry(a, b, carry);
 
 	    if (cur == BIT4_X) {
@@ -652,6 +652,9 @@ void vvp_shiftr::set(vvp_ipoint_t i, bool push, unsigned val, unsigned)
 
 /*
  * $Log: arith.cc,v $
+ * Revision 1.37  2005/01/30 05:06:49  steve
+ *  Get .arith/sub working.
+ *
  * Revision 1.36  2005/01/28 05:34:25  steve
  *  Add vector4 implementation of .arith/mult.
  *
diff --git a/vvp/compile.cc b/vvp/compile.cc
index 1af7128a7..cb72f05c3 100644
--- a/vvp/compile.cc
+++ b/vvp/compile.cc
@@ -17,7 +17,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #ifdef HAVE_CVS_IDENT
-#ident "$Id: compile.cc,v 1.184 2005/01/29 17:53:25 steve Exp $"
+#ident "$Id: compile.cc,v 1.185 2005/01/30 05:06:49 steve Exp $"
 #endif
 
 # include  "arith.h"
@@ -885,21 +885,13 @@ void compile_arith_sub(char*label, long wid, unsigned argc, struct symb_s*argv)
 {
       assert( wid > 0 );
 
-      if ((argc % wid) != 0) {
-	    fprintf(stderr, "%s; .arith has wrong number of symbols\n", label);
-	    compile_errors += 1;
-	    return;
-      }
-
-      unsigned opcount = argc / wid;
-      if (opcount > 4) {
-	    fprintf(stderr, "%s; .arith has too many operands.\n", label);
+      if (argc != 2) {
+	    fprintf(stderr, "%s .arith has wrong number of symbols\n", label);
 	    compile_errors += 1;
 	    return;
       }
 
       vvp_arith_ *arith = new vvp_arith_sub(wid);
-
       make_arith(arith, label, wid, argc, argv);
 }
 
@@ -1585,6 +1577,9 @@ void compile_param_string(char*label, char*name, char*str, char*value)
 
 /*
  * $Log: compile.cc,v $
+ * Revision 1.185  2005/01/30 05:06:49  steve
+ *  Get .arith/sub working.
+ *
  * Revision 1.184  2005/01/29 17:53:25  steve
  *  Use scheduler to initialize constant functor inputs.
  *
diff --git a/vvp/vvp_net.cc b/vvp/vvp_net.cc
index 27a530219..51ae6e396 100644
--- a/vvp/vvp_net.cc
+++ b/vvp/vvp_net.cc
@@ -16,7 +16,7 @@
  *    along with this program; if not, write to the Free Software
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
-#ident "$Id: vvp_net.cc,v 1.10 2005/01/29 17:52:06 steve Exp $"
+#ident "$Id: vvp_net.cc,v 1.11 2005/01/30 05:06:49 steve Exp $"
 
 # include  "vvp_net.h"
 # include  <stdio.h>
@@ -72,6 +72,18 @@ vvp_bit4_t operator & (vvp_bit4_t a, vvp_bit4_t b)
       return BIT4_1;
 }
 
+vvp_bit4_t operator ~ (vvp_bit4_t a)
+{
+      switch (a) {
+	  case BIT4_0:
+	    return BIT4_1;
+	  case BIT4_1:
+	    return BIT4_0;
+	  default:
+	    return  BIT4_X;
+      }
+}
+
 void vvp_send_vec4(vvp_net_ptr_t ptr, vvp_vector4_t val)
 {
       while (struct vvp_net_t*cur = ptr.ptr()) {
@@ -852,6 +864,9 @@ vvp_bit4_t compare_gtge_signed(const vvp_vector4_t&a,
 
 /*
  * $Log: vvp_net.cc,v $
+ * Revision 1.11  2005/01/30 05:06:49  steve
+ *  Get .arith/sub working.
+ *
  * Revision 1.10  2005/01/29 17:52:06  steve
  *  move AND to buitin instead of table.
  *
diff --git a/vvp/vvp_net.h b/vvp/vvp_net.h
index a0773e166..130177c66 100644
--- a/vvp/vvp_net.h
+++ b/vvp/vvp_net.h
@@ -18,7 +18,7 @@
  *    along with this program; if not, write to the Free Software
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
-#ident "$Id: vvp_net.h,v 1.10 2005/01/29 17:52:06 steve Exp $"
+#ident "$Id: vvp_net.h,v 1.11 2005/01/30 05:06:49 steve Exp $"
 
 # include  <assert.h>
 
@@ -52,7 +52,9 @@ enum vvp_bit4_t {
 extern vvp_bit4_t add_with_carry(vvp_bit4_t a, vvp_bit4_t b, vvp_bit4_t&c);
   /* Return TRUE if the bit is BIT4_X or BIT4_Z */
 extern bool bit4_is_xz(vvp_bit4_t a);
-  /* Some common boolean operators */
+  /* Some common boolean operators. These implement the Verilog rules
+     for 4-value bit operations. */
+extern vvp_bit4_t operator ~ (vvp_bit4_t a);
 extern vvp_bit4_t operator & (vvp_bit4_t a, vvp_bit4_t b);
 
 /*
@@ -507,6 +509,9 @@ class vvp_fun_signal  : public vvp_net_fun_t {
 
 /*
  * $Log: vvp_net.h,v $
+ * Revision 1.11  2005/01/30 05:06:49  steve
+ *  Get .arith/sub working.
+ *
  * Revision 1.10  2005/01/29 17:52:06  steve
  *  move AND to buitin instead of table.
  *