  Three (2+1)-dimensional equations, they are KP equation, cylindrical KP
equation and spherical KP equation, have been reduced to the same KdV equation
by different transformation of variables respectively. Since the single
solitary wave solution and 2-solitary wave solution of the KdV equation have
been known already, substituting the solutions of the KdV equation into the
corresponding transformation of variables respectively, the single and
2-solitary wave solutions of the three (2+1)-dimensional equations can be
obtained successfully.
