•For an ordinal a, will define Ja = { Ib, b < a } to have the
“back-and-forth” property
•
•Ib = a set of partial isomorphisms from A to
B
•
•Intuition: Ib contains set of
positions from which the duplicator can win
if only b rounds remain
•
•Intuition: duplicator has a winning strategy for a rounds iff there exists a set Ja with b&f
property