How incremental OTA works in AB oTA update

Question

I understood AB OTA work flow in android. I could not able to understanding, How incremental OTA works in AB update in AOSP.

 Full OTA_V0:
 A-->Active state
 B-->Inactive state

 Incremental OTA_V1:
 A-->Inactive state
 B-->Active state

 Incremental OTA_V2:
 A-->Active state(how incremental works here, because this slot is inactive in Incremental OTA_V1 ).
 B-->Inactive state

Thanks in advance.