  For It\^o stochastic equations in $\mathbb{R}^{d}$ with drift in $L_{d}$
several results are discussed such as the existence of weak solutions, the
existence of the corresponding Markov process, Aleksandrov type estimates of
their Green's functions, which yield their summability to the power of
$d/(d-1)$, the Fabes-Stroock type estimates which show that Green's functions
are summable to a higher degree, the Fanghua Lin type estimates, which are one
of the main tools in the $W^{2}_{p}$-theory of fully nonlinear elliptic
equations, the fact that Green's functions are in the class $A_{\infty}$ of
Muckenhoupt and a few other results.
