Note that if (5′) were established, we would have settled the matter. After all, with a straightforward reworking of (ME#) (namely, If ☐(NBG → ∃f A1…An such that there is no model for (A1∧…∧An)), then ¬◊(A1 ∧…∧ An)), it follows from (5′) and (ME#) that