19
Why we care: 2
•
Satsfiability
•
Given
f
, decide if
9
A s.t. A
²
f
•
•
Undecidable for FO
(Trakhtenbrot)
•
Decidable for FO
2
(WOW !)
•
Undecidable for FO
3
(Hmm….)