@unpublished{repository42070,
           title = {Bukti ajar prinsip sistem},
       publisher = {Universitas Muhammadiyah Prof. Dr. Hamka},
            note = {Unpublished},
             url = {http://repository.uhamka.ac.id/id/eprint/42070/},
          author = {Hamid Al Jufri, Jufri}
}