6
Problem 3
•
f
(R,
x
) is monotone in R if for any two
structures
A
,
B
s.t. R
A
µ
R
B
, A=B, and
S
A
=S
B
for any other relation name S,
{
a
|
A
²
f
}
µ
{
a
|
B
²
f
}
•
•
Prove that it is undecidable if a formula
f
(R,
x
) is monotone in R
•
•