2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/39915The cross section near the $t\bar t$ production threshold in $e^+e^-$ annihilation and $γγ$ collisions is discussed. The NNLO results within NRQCD are briefly overviewed.17 pages, latex, 1 figure. Talk presented at Quarks-2000 Seminar, Pushkin, Russia, May 13-21, 2000High Energy Physics - PhenomenologyHigh Energy Physics - Experimenttext