12 Logical Timestamps

Happened Before

A → B "A happens-before B"

Transitivity: If A→B, and B→C, we can say A→C.

Two events are concurrent (denoted as || ) if: A ⇏B and B⇏A. (⇏ means “not
Happened-Before”).

In the above example we can say: a→b, b→c, x→y,y→z from the ordering of events on
individual processes.

We can also say: b→y and z→c from the ordering of send/recieve events.

This means, from transitivity, we can say a→y and b→z for example (and many more).

However, when considering a and x, a ⇏ x and x⇏a. Thus, these two events are concurrent (x||a).