XID comparations

Hi,

I would like to understand better the logic to determine when a xid is older
than another one.

As I could understand, the XID is always incremented, never reset. If it is
true, then we can have rows with cmin ranging
from 1 to 4.294.967.295 (2^32-1).

When xid overflows (32 bits) the next one will be 3 (1 and 2 are reserved).

In this case, we could have have lines with cmin 4.294.967.295 and lines
with cmin 3. How are they compared to determine that
rows with cmin 3 are newer than rows with cmin 4.294.967.295?

Thanks in advance,

Reimer