CAP theorem

http://ksat.me/a-plain-english-introduction-to-cap-theorem/ 

CA => Consistent and available

C => same state

A => every request should receive a response

P => any number of messages in intercom can be lost

If

C => same state

AND

A => every request should receive a response, so every write request should be Success or Failure

THEN

!P => since you can't lose intercom messages

CP

If

C => same state

AND

P => any number of messages in intercom can be lost

THEN

!A => can't respond to write requests since there is no assurance of being C as the messages are lost

AP

A=> take write requests and respond

AND

P => any number of messages in intercom can be lost

THEN

!C => in absence of communication they will be in different states.

http://blog.thislongrun.com/2015/04/the-unclear-cp-vs-ca-case-in-cap.html