Definition nextIndex_preserved st st' :=
    (type st' = Leader ->
     type st = Leader /\
     maxIndex (log st) <= maxIndex (log st') /\
     nextIndex st' = nextIndex st).

Lemma handleRequestVote_nextIndex_preserved : forall st h h' t lli llt st' m, handleRequestVote h st t h' lli llt = (st', m) -> nextIndex_preserved st st'.