module inv_mux(out, cnt, a, b);

   output out;
   input  cnt, a, b;

   assign out = (cnt) ? ~b : ~a;

endmodule // inv_mux


module stimulus;
   reg	cnt, a, b;
   wire	out;
   integer i;

   inv_mux i_m (out, cnt, a, b);

   initial begin
      $display($time, " cnt a  b  - out");
      for (i = 0; i < 8; i = i + 1) begin
	 {cnt, a, b} = i[2:0];
	 #10 $display ($time, "  %b  %b  %b  -  %b", cnt, a, b, out);
      end
      #10 $finish;
   end // initial begin

endmodule // stimulus