Ulam matrix on omega-one
= Ulam matrix on omega-one
{c}
{title2=$(A_{\alpha,n})$}
A family $(A_{\alpha,n})_{\alpha<\omega_1,n<\omega}$ whose row at $\alpha$ partitions $(\alpha,\omega_1)$ and whose fixed-column cells are pairwise disjoint. Choose <injections> $e_\beta:\beta\to\omega$ and put $A_{\alpha,n}=\{\beta>\alpha:e_\beta(\alpha)=n\}$. This gives a matrix used to split <stationary sets> into many stationary pieces.