Creating Coverpoint using with clause

 Hi,

   I am unable to to create a coverpoint using with it is giving an error . My code is as

   cp_in1 : coverpoint in1 {

        bins b1[ = in1 with ($countones(item) == 3);

   }

  Here in1 is a 8-bit variable. I am using INCISIV 13.10.013.

  So please tell me how do i create the point for this.

Thanks

Srikanth M.