In a application , four processes P1, P2, P3 and P4. By using vector clock to timestamp their local event.

• P1: a(1,0,0,0),b(2,0,0,0).
• P2: c(2,1,0,0),d(2,2,0,0).
• P3: e(0,0,1,0),f(2,3,3,3).
• P4: g(0,0,1,1),h(0,0,1,2).

What are the pairs of event that are concurrent using the happen-before relation notation? diagram example will be good thank you