  The contribution of the electron-electron interaction to conductivity is
analyzed step by step in gated GaAs/InGaAs/GaAs heterostructures with different
starting disorder. We demonstrate that the diffusion theory works down to $k_F
l\simeq 1.5-2$, where $k_F$ is the Fermi quasimomentum, $l$ is the mean free
paths. It is shown that the e-e interaction gives smaller contribution to the
conductivity than the interference independent of the starting disorder and its
role rapidly decreases with $k_Fl$ decrease.
