you can check the attachment

Trypsin is a protease, degrading cell adhesion molecules and thus detaching the from substrate and each other. And Versene is EDTA solution in PBS, that disrupts cell adhesion molecules binding chelating necessary divalent cations. Trypsin and EDTA can act sinergically, thus the lower concentration of each is needed for cell detachment in their mixture. Versene solution is considered to detach the cells milder, than trypsin, because the cells don't need to restore their adhesion molecules after detachment.