Artikel Jurnal
Popper, Karl R.
Basic Books, 1959
Buku Teks SO
Cohen, Morris R.
Harcourt, Brace & World, 1934
Buku Teks SO
Epstein, Richard A.
Academic Press, 1977
Buku Teks SO
The Society for Industrial and Applied Mathematics , 2018
Majalah, Jurnal, Buletin