@book{ref1,
         author ={author1},
         title = {title of the book},
         year =year,
         publisher = "publisher",
         address = "publisher's address",
}

@book{ref2,
         author ={author1},
         title = {title of the book},
         year =year,
         publisher = "publisher",
         address = "publisher's address",
}

@book{ref3,
         author ={author1},
         title = {title of the book},
         year =year,
         publisher = "publisher",
         address = "publisher's address",
}

@book{ref10,
         author ={author1},
         title = {title of the book},
         year =year,
         publisher = "publisher",
         address = "publisher's address",
}

@book{ref11,
         author ={author1},
         title = {title of the book},
         year =year,
         publisher = "publisher",
         address = "publisher's address",
}

@book{ref12,
         author ={author1},
         title = {title of the book},
         year =year,
         publisher = "publisher",
         address = "publisher's address",
}

@article{ref4,
        author = {authors1 and authors2},
        title = {title of the article},
        journal = journal name,
        year =year,
        volume =volume,
        number =number,
        pages = "pages-pages",
}

@article{ref5,
        author = {authors1 and authors2},
        title = {title of the article},
        journal = journal name,
        year =year,
        volume =volume,
        number =number,
        pages = "pages-pages",
}

@article{ref6,
        author = {authors1 and authors2},
        title = {title of the article},
        journal = journal name,
        year =year,
        volume =volume,
        number =number,
        pages = "pages-pages",
}

@inproceedings{ref7,
         author = {authors1, authors2, authors3 and authors4},
         title = {Title of work},
         booktitle =title,
         address={address},
         year =year,
         month="month",
         pages = "pages-pages",
}

@inproceedings{ref8,
         author = {authors1, authors2, authors3 and authors4},
         title = {Title of work},
         booktitle =title,
         address={address},
         year =year,
         month="month",
         pages = "pages-pages",
}

@inproceedings{ref9,
         author = {authors1, authors2, authors3 and authors4},
         title = {Title of work},
         booktitle =title,
         address={address},
         year =year,
         month="month",
         pages = "pages-pages",
}