With the public key of the authority, the authenticity of every tallying
key is verified in 3.2 by checking the signature on it. And from 3.3,
with the published validated tallying keys, the signatures on encrypted
ballot 
, and on key 
can also be verified universally,
especially by the tallier. So, only the voters who hold the validated voting
keys, of which
the corresponding tallying keys are signed by the authority in registration
phase, can cast valid ballots.
Without the voting key 
, none can change the ballot associated
with the corresponding published tallying key 
, unless voter
V who holds 
want to change his or her mind in voting period
if the election policy allow voters to change their minds within a certain
period of time. Miscounting a ballot can will be discovered by the voter
in 3.3 without revealing the ballot.
Moreover, since the validated tallying keys are published, none can cast
votes for abstaining voters.