Verkuly, H.J.
het spectrum, [date of publication not identified]
Buku Teks
Denninghaus, F.
Verlag Lambert Lensing GMBH, 972
Buku Teks
Barentsen, A. A., author
Moeder , 1985
Buku Teks
Lusin, Natala
Baron's Education, 1992
Buku Referensi
Smirnitsky, A.I., author
Higher School Publishing House, 1975
Buku Teks