anchor.diff:        dec_wire <= x;
      endmethod
      method ActionValue#(Bool) maybeDecrement(UInt#(count_sz) x);
  -      if (cnt + inc_wire >= x) begin
  +      if (cnt >= x) begin
   	 dec_wire <= x;
   	 return True;
         end
  
positive.code:    method ActionValue#(Bool) maybeDecrement(UInt#(count_sz) x);
     method Action increment(UInt#(count_sz) x);
     method UInt#(count_sz) read();
     method Bool positive();
  endinterface
  
  
negative.code:    Reg#(Bool) positive_reg <- mkReg(False);
     (* fire_when_enabled *)
     rule react;
        let new_count = (cnt + inc_wire) - dec_wire;
        cnt <= new_count;
        positive_reg <= (new_count > 0);
     endrule
  