@startuml
title msc example1 (abstracted m2)
autonumber

' Define participants
participant i1
participant i2
participant i3
participant i4
boundary Environment

' i1 outputs m0 to the environment
i1 -> Environment: m0

' i1 sends m1 to i2
i1 -> i2: m1

' Local action 'a' on i2
' (Originally this was after m2, now it is just after m1)
note right of i2: action a

' m2 is ABSTRACTED AWAY (Removed)
' i2 -> i3: m2  <-- DELETED
' i3 receives m2 <-- DELETED

' i2 sends m4 back to i1
i2 -> i1: m4

' i3 sends m3 to i4
' (Originally this happened after receiving m2. 
' Now it is independent and can happen concurrently with the i1/i2 interactions)
i3 -> i4: m3

@enduml