[11] Niven, I., Zuckerman, H.S.: Einführung in die Zahlentheorie. 1975, Bibliograph. Inst., Mannheim, 
[12] Nowak, W.G.: 
On simultaneous Diophantine approximation. Rend. Circ. Mat. Palermo, Ser. II, 33, 1984, 456-460,  
MR 0779948 | 
Zbl 0535.10036 
[13] Nowak, W.G.: 
The critical determinant of the double paraboloid and Diophantine approximation in ${\fam 5 R}^3$ and ${\fam 5 R}^4$. Math. Pannonica, 10, 1999, 111-122,  
MR 1678107 
[14] Nowak, W.G.: 
Diophantine approximation in ${\fam 5 R}^s$: On a method of Mordell and Armitage. Algebraic number theory and Diophantine analysis. Proceedings of the conference held in Graz, Austria, August 30 to September 5, 1998, 2000, 339-349, W. de Gruyter, Berlin,  
MR 1770472 
[15] Prasad, A.V.: 
Simultaneous Diophantine approximation. Proc. Indian Acad. Sci. A, 31, 1950, 1-15,  
MR 0036270 | 
Zbl 0036.30801 
[16] Spohn, W.G.: 
Blichfeldt's theorem and simultaneous Diophantine approximation. Amer. J. Math., 90, 1968, 885-894,  
DOI 10.2307/2373489 | 
MR 0231794