10
Ehrenfeucht-Fraisse Games
•Given two structures A, B
•Two players: spoiler and duplicator play k rounds
•
•Round i  (i =1, …, k):
1.Spoiler picks a structure A or B
2.Spoiler picks an element in that structure ai 2 A or bi 2 B
3.Duplicator responds by picking an element in the other structure, bi 2 B or ai 2 A
•Duplicator wins if a, b is a partial isomorphism