  The first two sections of this work review the framework of [6] for
approximate solutions of the incompressible Euler or Navier-Stokes (NS)
equations on a torus T^d, in a Sobolev setting. This approach starts from an
approximate solution u_a of the Euler/NS Cauchy problem and, analyzing it a
posteriori, produces estimates on the interval of existence of the exact
solution u and on the distance between u and u_a. The next two sections present
an application to the Euler Cauchy problem, where u_a is a Taylor polynomial in
the time variable t; a special attention is devoted to the case d=3, with an
initial datum for which Behr, Necas and Wu have conjectured a finite time
blowup [1]. These sections combine the general approach of [6] with the
computer algebra methods developed in [9]; choosing the Behr-Necas-Wu datum,
and using for u_a a Taylor polynomial of order 52, a rigorous lower bound is
derived on the interval of existence of the exact solution u, and an estimate
is obtained for the H^3 Sobolev distance between u(t) and u_a(t).
