Hehe, guys, I realize that
The real question is: why do we need the PostStep?
For finishing the iteration. For example, you might have state variables to reset again at the end of the time step. Or you might need to log parameters.
One design example from my Frankensteins Lab: You have a radio communication library, that works by letting vessels send messages and receive them via message buffers. In the time step, all spacecraft should receive all messages for them by other spacecraft via message queues.
As you can see, this isn't done with pre-step alone, you design the library that the messages in the communication object are sent in prestep and received and handled in Post-Step. Now all spacecraft can send their messages in one phase and receive them in the other, but still all happens in the same timestep and not for example, that the first spacecraft in Orbiters vessel list receives the messages of the last spacecraft in the next timestep, while the last spacecraft receives the messages from the first spacecraft already in the same timestep. Sounds harmless when you only have two spacecraft, but once you have three or more, the situation becomes much more annoying, without using post-step.
