@book{Smith.2020,
    author = {John Smith},
    title = {A Comprehensive Introduction to C++},
    year = {2020},
    publisher = {Tech Books Publishing Ltd.},
    address = {New York},
}

@book{a,
    author = {John Smith},
    title = {A Comprehensive Introduction to C++},
    year = {2020},
    publisher = {Tech Books Publishing Ltd.},
    address = {New York},
}

@book{b,
    author = {John Smith},
    title = {A Comprehensive Introduction to C++},
    year = {2020},
    publisher = {Tech Books Publishing Ltd.},
    address = {New York},
}

@book{c,
    author = {John Smith},
    title = {A Comprehensive Introduction to C++},
    year = {2020},
    publisher = {Tech Books Publishing Ltd.},
    address = {New York},
}
@book{d,
    author = {John Smith},
    title = {A Comprehensive Introduction to C++},
    year = {2020},
    publisher = {Tech Books Publishing Ltd.},
    address = {New York},
}