F0 Tenses

F0 has relative tense prefixes in addition to absolute tense prefixes 
and and the aspect suffixes. The relative tenses are

present (unmarked),
immediate past,
indefinite past, and
indefinite future.

The relative tenses are used by themselves on dependent verbs. They 
combine with the absolute tenses on independent verbs. The absolute 
tenses are present and definite non-present. The combinations are:

(1) A present + R present = jussive if the verb is perfective, else 
absolute present
(2) A present + R immediate past = absolute immediate past
(3) A present + R indefinite past = present retrospective if perfective, 
else indefinite past
(4) A present + R indefinite future = present prospective if perfective, 
else indefinite future
(5) A non-present + R present = definite past or future, depending on 
(6) A non-present + R indefinite past = past or future retrospective, 
depending on context
(7) A non-present + R indefinite future = past or future prospective, 
depending on context

The last two apply only to perfective verb forms.