412. Infinitives, words and expressions quoted or explained, and letters
of the alphabet, are neuter: as,
#vīvere ipsum#, _mere living_; #istūc ‘taceō,’# _your ‘I won’t
mention;’_ #longum vale#, _a long goodbye_; #o Graecum#, _Greek O_. But
the letters have sometimes a feminine adjective, agreeing with #littera#
understood.