@unpublished{repository40736,
           title = {sertifikat PPI UUM},
            note = {Unpublished},
       publisher = {Universitas Muhammadiyah Prof.DR.HAMKA},
             url = {http://repository.uhamka.ac.id/id/eprint/40736/},
          author = {Zulherman, Zulherman}
}