The Back-and-Forth Property
•What
does A
'k B
say ?
•
•If we
have a partial isomorphism from (A,
a1,
…, ai) to (B,b1,
…, bi), where i < k, and ai+1 2 A,
then there exists bi+1 2 B
s.t. there exists a partial isomorphism from (A, a1,
…, ai,
ai+1)
to (B,
b1,
…, bi, bi+1); and vice versa