  A class of (1+2)-dimensional diffusion-convection equations (nonlinear
Kolmogorov equations) with time-dependent coefficients is studied with Lie
symmetry point of view. The complete group classification is achieved using a
gauging of arbitrary elements (i.e. via reducing the number of variable
coefficients) with the application of equivalence transformations. Two possible
gaugings are discussed in detail in order to show how equivalence groups serve
in making the optimal choice.
