We establish the conjecture of Reiner and Yong for an explicit combinatorial formula expansion a Grothendieck polynomial into basis Lascoux polynomials. This is subtle refinement its symmetric function version due to Buch, Kresch, Shimozono, Tamvakis, Yong, which gives stable polynomials indexed by permutations Grassmannian Our <mml:math xmlns:mml="ht...