All the evidence so far gathered fits both Dr  Grippen' s theory and Professor Heissmann' s  However, the predictions that these theories make about the result of the planned experiment cannot both be true
Ttherefore, the result of this experiment will confirm one of these theories at the expense of the other
David thinks this tree is a beech. Jane thinks it is an elm. Maria, unlike David or Jane, is expert at tree identification, so when Maria gives her opinion it will verify either David's or Jane's opinion.