Definition mkEFF
            (NB2':block)
            (Hyp1: (Mem.nextblock m2 <= NB2')%positive)
            (Hyp2: forall (b1 b2 : block) (delta : Z),
                       j12' b1 = Some (b2, delta) -> (b2 < NB2')%positive)
           : Mem.mem'.

Lemma mkEff_nextblock: forall N Hyp1 Hyp2, Mem.nextblock (mkEFF N Hyp1 Hyp2) = N.