Instability and non-uniqueness in the Cauchy problem for the Euler equations of an ideal incompressible fluid. Part I

In Part I of the paper, we prove non-uniqueness of the solution to the Cauchy problem of the Euler equations of an ideal incompressible fluid in dimension two with vorticity in some Lebesgue space. The radially symmetric external force is locally integrable with values in the same Lebesgue space.