16
Fixed Point Logics
•
s
= vocabulary, R
Ï
s
•
•
Let
f
(R,
x
) be a formula over
s
[
{R}
here |
x
| = arity(R)
•
[that is,
x
are
all
the free variables in
f
]
•
Define three new formulas:
[
lfp
R, x
f
(R,
x
)][
t
]
[
ifp
R, x
f
(R,
x
)][
t
]
[
pfp
R, x
f
(R,
x
)][
t
]
