On an effective proof of the Oppenheim conjecture.

In the mid eighties I proved the Oppenheim conjecture about the values of indefinite irrational quadratic forms in $n>2$ variables. The proof used the notion of a minimal set and some limiting constructions and because of that was not effective. I am planning to explain some ingredients of recent joint work with E.Lindenstrauss which provides effective estimates for the size of the smallest nonzero integral solution of the inequality
$|Q(x)|< a$ in terms of the diophantine properties of coefficents of $Q$.