Assembly of the regular-annulus lemma #
lem:aniso:annulus is the paper's regular-annulus lemma: from a suitable weak solution smooth on
compact subsets of Q with a C²-bounded force, and radii R₁ < R₀ < 1, it produces a strictly
smaller annulus and a time t₀ on which u, ∇u, ∇²u are bounded, and a circulation bound on
every sub-radius. It has three ingredients: the choice of the annulus via the null Hausdorff
measure of the singular set (exists_annulus_bound_of_timeZeroSingularSetNull), the circulation
bound from an order-0 velocity bound (forall_Rstar_exists_circulation_bound_of_annulus_bound),
and the interior derivative estimate for the Navier–Stokes system (Serrin, Section 4, m = 1). The
*_conditional_on_serrin statements take the last as an explicit hypothesis hserrin, as
step_annulus_derivative_bounds does; CIV.Main.regularAnnulus discharges it with
CIV.Main.serrinInteriorEstimates. In this file the circulation bound is restricted to the
annulus Rm < |x| < Rstar that forall_Rstar_exists_circulation_bound_of_annulus_bound
delivers; exists_annulus_bound_wholeBall_conditional_on_serrin gives it on the full ball
B(Rstar), as stated in the manuscript.