5
Consequence 2
•
Definition
. A sentence
f
is
finitely valid
,
²
fin
f
, if for all finite models
A
,
A
²
f
•
•
Question:
is there a complete proof system
`
,
i.e.
such that
`
f
iff
²
fin
f
?
•
•
Answer:
NO !
[why ?]