2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/42761It is shown that the linear correlation relates the S-wave phase shifts from the threshold up to dipion mass 900 MeV. By using this correlation at the solution of the Roy equations, the accuracy of determination of S-wave lengths is considerably improved. The obtained result unambiguously witnesses in favor of the standard ChPT version with large quark condensate.8 pages, 4 postscript figures, LaTeX; typos corrected, references updated and expanded, added more material in Sect.3High Energy Physics - Phenomenologytext