16
Fagin’s Theorem
•
Need encodings of finite structures:
•
Let
A
= (A, R
1
A
, …, R
p
A
)
where A = {a
1
, …, a
n
}
•
Fix an order a
1
< a
2
< … < a
n
•
where each enc(R
i
A
) is a string of length n
k
in {0,1}
*
[what meaning ? See book pp. 88]
enc(
A
) = 0
n
˘
1
˘
enc(R
1
A
)
˘
˘
˘
enc(R
p
A
)