22
FO+TrCl
•
Definition
Transitive closure.
Let
f
(
x
,
y
,
z
) be a formula, where |
x
| = |
y
| =
k, and
t
1
,
t
2
are tuples of length k.
Then:
[
trcl
x, y
f
(
x
,
y
,
z
)](
t
1
,
t
2
)
is a formula with free variables
z
.