H. Davenport and W. M. Schmidt, Approximation to real numbers by algebraic integers, Acta Arithmetica, vol.15, pp.393-416, 1969.

O. N. German, Transference inequalities for multiplicative diophantine exponents, Proceedings of the Steklov Institute of Mathematics, vol.275, issue.1, pp.275227-239, 2011.
DOI : 10.1134/S0081543811080153

S. Harrap, Twisted inhomogeneous Diophantine approximation and badly approximable sets, Acta Arithmetica, vol.151, issue.1, pp.55-82, 2012.
DOI : 10.4064/aa151-1-5
URL : http://arxiv.org/abs/1003.2362

M. Laurent, Exponents of diophantine approximmation in dimension two. Canad, J. Math, vol.61, pp.165-189, 2009.

H. Minkowski, Geometrie der Zahlen Bibliotheca Mathematica Teubneriana , Band 40, Johnson Reprint Corp, 1968.