10
Normal Form
•
Every IFP or LFP formula is equivalent to one
formula “with only one LFP, at the top”:
9
x
1
…
9
x
k
.
lfp
R
[
f
](
x
)
where
f
is in FO (i.e. without fixpoints)
•
Proof: in the book (not hard),
but better see next